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+*usr_41.txt*	For Vim version 7.0aa.  Last change: 2004 May 06
+
+		     VIM USER MANUAL - by Bram Moolenaar
+
+			      Write a Vim script
+
+
+The Vim script language is used for the startup vimrc file, syntax files, and
+many other things.  This chapter explains the items that can be used in a Vim
+script.  There are a lot of them, thus this is a long chapter.
+
+|41.1|	Introduction
+|41.2|	Variables
+|41.3|	Expressions
+|41.4|	Conditionals
+|41.5|	Executing an expression
+|41.6|	Using functions
+|41.7|	Defining a function
+|41.8|	Exceptions
+|41.9|	Various remarks
+|41.10|	Writing a plugin
+|41.11|	Writing a filetype plugin
+|41.12|	Writing a compiler plugin
+
+     Next chapter: |usr_42.txt|  Add new menus
+ Previous chapter: |usr_40.txt|  Make new commands
+Table of contents: |usr_toc.txt|
+
+==============================================================================
+*41.1*	Introduction					*vim-script-intro*
+
+Your first experience with Vim scripts is the vimrc file.  Vim reads it when
+it starts up and executes the commands.  You can set options to values you
+prefer.  And you can use any colon command in it (commands that start with a
+":"; these are sometimes referred to as Ex commands or command-line commands).
+   Syntax files are also Vim scripts.  As are files that set options for a
+specific file type.  A complicated macro can be defined by a separate Vim
+script file.  You can think of other uses yourself.
+
+Let's start with a simple example: >
+
+	:let i = 1
+	:while i < 5
+	:  echo "count is" i
+	:  let i = i + 1
+	:endwhile
+<
+	Note:
+	The ":" characters are not really needed here.  You only need to use
+	them when you type a command.  In a Vim script file they can be left
+	out.  We will use them here anyway to make clear these are colon
+	commands and make them stand out from Normal mode commands.
+
+The ":let" command assigns a value to a variable.  The generic form is: >
+
+	:let {variable} = {expression}
+
+In this case the variable name is "i" and the expression is a simple value,
+the number one.
+   The ":while" command starts a loop.  The generic form is: >
+
+	:while {condition}
+	:  {statements}
+	:endwhile
+
+The statements until the matching ":endwhile" are executed for as long as the
+condition is true.  The condition used here is the expression "i < 5".  This
+is true when the variable i is smaller than five.
+   The ":echo" command prints its arguments.  In this case the string "count
+is" and the value of the variable i.  Since i is one, this will print:
+
+	count is 1 ~
+
+Then there is another ":let i =" command.  The value used is the expression "i
++ 1".  This adds one to the variable i and assigns the new value to the same
+variable.
+   The output of the example code is:
+
+	count is 1 ~
+	count is 2 ~
+	count is 3 ~
+	count is 4 ~
+
+	Note:
+	If you happen to write a while loop that keeps on running, you can
+	interrupt it by pressing CTRL-C (CTRL-Break on MS-Windows).
+
+
+THREE KINDS OF NUMBERS
+
+Numbers can be decimal, hexadecimal or octal.  A hexadecimal number starts
+with "0x" or "0X".  For example "0x1f" is 31.  An octal number starts with a
+zero.  "017" is 15.  Careful: don't put a zero before a decimal number, it
+will be interpreted as an octal number!
+   The ":echo" command always prints decimal numbers.  Example: >
+
+	:echo 0x7f 036
+<	127 30 ~
+
+A number is made negative with a minus sign.  This also works for hexadecimal
+and octal numbers.   A minus sign is also for subtraction.  Compare this with
+the previous example: >
+
+	:echo 0x7f -036
+<	97 ~
+
+White space in an expression is ignored.  However, it's recommended to use it
+for separating items, to make the expression easier to read.  For example, to
+avoid the confusion with a negative number, put a space between the minus sign
+and the following number: >
+
+	:echo 0x7f - 036
+
+==============================================================================
+*41.2*	Variables
+
+A variable name consists of ASCII letters, digits and the underscore.  It
+cannot start with a digit.  Valid variable names are:
+
+	counter
+	_aap3
+	very_long_variable_name_with_underscores
+	FuncLength
+	LENGTH
+
+Invalid names are "foo+bar" and "6var".
+   These variables are global.  To see a list of currently defined variables
+use this command: >
+
+	:let
+
+You can use global variables everywhere.  This also means that when the
+variable "count" is used in one script file, it might also be used in another
+file.  This leads to confusion at least, and real problems at worst.  To avoid
+this, you can use a variable local to a script file by prepending "s:".  For
+example, one script contains this code: >
+
+	:let s:count = 1
+	:while s:count < 5
+	:  source other.vim
+	:  let s:count = s:count + 1
+	:endwhile
+
+Since "s:count" is local to this script, you can be sure that sourcing the
+"other.vim" script will not change this variable.  If "other.vim" also uses an
+"s:count" variable, it will be a different copy, local to that script.  More
+about script-local variables here: |script-variable|.
+
+There are more kinds of variables, see |internal-variables|.  The most often
+used ones are:
+
+	b:name		variable local to a buffer
+	w:name		variable local to a window
+	g:name		global variable (also in a function)
+	v:name		variable predefined by Vim
+
+
+DELETING VARIABLES
+
+Variables take up memory and show up in the output of the ":let" command.  To
+delete a variable use the ":unlet" command.  Example: >
+
+	:unlet s:count
+
+This deletes the script-local variable "s:count" to free up the memory it
+uses.  If you are not sure if the variable exists, and don't want an error
+message when it doesn't, append !: >
+
+	:unlet! s:count
+
+When a script finishes, the local variables used there will not be
+automatically freed.  The next time the script executes, it can still use the
+old value.  Example: >
+
+	:if !exists("s:call_count")
+	:  let s:call_count = 0
+	:endif
+	:let s:call_count = s:call_count + 1
+	:echo "called" s:call_count "times"
+
+The "exists()" function checks if a variable has already been defined.  Its
+argument is the name of the variable you want to check.  Not the variable
+itself!  If you would do this: >
+
+	:if !exists(s:call_count)
+
+Then the value of s:call_count will be used as the name of the variable that
+exists() checks.  That's not what you want.
+   The exclamation mark ! negates a value.  When the value was true, it
+becomes false.  When it was false, it becomes true.  You can read it as "not".
+Thus "if !exists()" can be read as "if not exists()".
+   What Vim calls true is anything that is not zero.  Only zero is false.
+
+
+STRING VARIABLES AND CONSTANTS
+
+So far only numbers were used for the variable value.  Strings can be used as
+well.  Numbers and strings are the only two types of variables that Vim
+supports.  The type is dynamic, it is set each time when assigning a value to
+the variable with ":let".
+   To assign a string value to a variable, you need to use a string constant.
+There are two types of these.  First the string in double quotes: >
+
+	:let name = "peter"
+	:echo name
+<	peter ~
+
+If you want to include a double quote inside the string, put a backslash in
+front of it: >
+
+	:let name = "\"peter\""
+	:echo name
+<	"peter" ~
+
+To avoid the need for a backslash, you can use a string in single quotes: >
+
+	:let name = '"peter"'
+	:echo name
+<	"peter" ~
+
+Inside a single-quote string all the characters are taken literally.  The
+drawback is that it's impossible to include a single quote.  A backslash is
+taken literally as well, thus you can't use it to change the meaning of the
+character after it.
+   In double-quote strings it is possible to use special characters.  Here are
+a few useful ones:
+
+	\t		<Tab>
+	\n		<NL>, line break
+	\r		<CR>, <Enter>
+	\e		<Esc>
+	\b		<BS>, backspace
+	\"		"
+	\\		\, backslash
+	\<Esc>		<Esc>
+	\<C-W>		CTRL-W
+
+The last two are just examples.  The  "\<name>" form can be used to include
+the special key "name".
+   See |expr-quote| for the full list of special items in a string.
+
+==============================================================================
+*41.3*	Expressions
+
+Vim has a rich, yet simple way to handle expressions.  You can read the
+definition here: |expression-syntax|.  Here we will show the most common
+items.
+   The numbers, strings and variables mentioned above are expressions by
+themselves.  Thus everywhere an expression is expected, you can use a number,
+string or variable.  Other basic items in an expression are:
+
+	$NAME		environment variable
+	&name		option
+	@r		register
+
+Examples: >
+
+	:echo "The value of 'tabstop' is" &ts
+	:echo "Your home directory is" $HOME
+	:if @a > 5
+
+The &name form can be used to save an option value, set it to a new value,
+do something and restore the old value.  Example: >
+
+	:let save_ic = &ic
+	:set noic
+	:/The Start/,$delete
+	:let &ic = save_ic
+
+This makes sure the "The Start" pattern is used with the 'ignorecase' option
+off.  Still, it keeps the value that the user had set.
+
+
+MATHEMATICS
+
+It becomes more interesting if we combine these basic items.  Let's start with
+mathematics on numbers:
+
+	a + b		add
+	a - b		subtract
+	a * b		multiply
+	a / b		divide
+	a % b		modulo
+
+The usual precedence is used.  Example: >
+
+	:echo 10 + 5 * 2
+<	20 ~
+
+Grouping is done with braces.  No surprises here.  Example: >
+
+	:echo (10 + 5) * 2
+<	30 ~
+
+Strings can be concatenated with ".".  Example: >
+
+	:echo "foo" . "bar"
+<	foobar ~
+
+When the ":echo" command gets multiple arguments, it separates them with a
+space.  In the example the argument is a single expression, thus no space is
+inserted.
+
+Borrowed from the C language is the conditional expression:
+
+	a ? b : c
+
+If "a" evaluates to true "b" is used, otherwise "c" is used.  Example: >
+
+	:let i = 4
+	:echo i > 5 ? "i is big" : "i is small"
+<	i is small ~
+
+The three parts of the constructs are always evaluated first, thus you could
+see it work as:
+
+	(a) ? (b) : (c)
+
+==============================================================================
+*41.4*	Conditionals
+
+The ":if" commands executes the following statements, until the matching
+":endif", only when a condition is met.  The generic form is:
+
+	:if {condition}
+	   {statements}
+	:endif
+
+Only when the expression {condition} evaluates to true (non-zero) will the
+{statements} be executed.  These must still be valid commands.  If they
+contain garbage, Vim won't be able to find the ":endif".
+   You can also use ":else".  The generic form for this is:
+
+	:if {condition}
+	   {statements}
+	:else
+	   {statements}
+	:endif
+
+The second {statements} is only executed if the first one isn't.
+   Finally, there is ":elseif":
+
+	:if {condition}
+	   {statements}
+	:elseif {condition}
+	   {statements}
+	:endif
+
+This works just like using ":else" and then "if", but without the need for an
+extra ":endif".
+   A useful example for your vimrc file is checking the 'term' option and
+doing something depending upon its value: >
+
+	:if &term == "xterm"
+	:  " Do stuff for xterm
+	:elseif &term == "vt100"
+	:  " Do stuff for a vt100 terminal
+	:else
+	:  " Do something for other terminals
+	:endif
+
+
+LOGIC OPERATIONS
+
+We already used some of them in the examples.  These are the most often used
+ones:
+
+	a == b		equal to
+	a != b		not equal to
+	a >  b		greater than
+	a >= b		greater than or equal to
+	a <  b		less than
+	a <= b		less than or equal to
+
+The result is one if the condition is met and zero otherwise.  An example: >
+
+	:if v:version >= 600
+	:  echo "congratulations"
+	:else
+	:  echo "you are using an old version, upgrade!"
+	:endif
+
+Here "v:version" is a variable defined by Vim, which has the value of the Vim
+version.  600 is for version 6.0.  Version 6.1 has the value 601.  This is
+very useful to write a script that works with multiple versions of Vim.
+|v:version|
+
+The logic operators work both for numbers and strings.  When comparing two
+strings, the mathematical difference is used.  This compares byte values,
+which may not be right for some languages.
+   When comparing a string with a number, the string is first converted to a
+number.  This is a bit tricky, because when a string doesn't look like a
+number, the number zero is used.  Example: >
+
+	:if 0 == "one"
+	:  echo "yes"
+	:endif
+
+This will echo "yes", because "one" doesn't look like a number, thus it is
+converted to the number zero.
+
+For strings there are two more items:
+
+	a =~ b		matches with
+	a !~ b		does not match with
+
+The left item "a" is used as a string.  The right item "b" is used as a
+pattern, like what's used for searching.  Example: >
+
+	:if str =~ " "
+	:  echo "str contains a space"
+	:endif
+	:if str !~ '\.$'
+	:  echo "str does not end in a full stop"
+	:endif
+
+Notice the use of a single-quote string for the pattern.  This is useful,
+because backslashes need to be doubled in a double-quote string and patterns
+tend to contain many backslashes.
+
+The 'ignorecase' option is used when comparing strings.  When you don't want
+that, append "#" to match case and "?" to ignore case.  Thus "==?" compares
+two strings to be equal while ignoring case.  And "!~#" checks if a pattern
+doesn't match, also checking the case of letters.  For the full table see
+|expr-==|.
+
+
+MORE LOOPING
+
+The ":while" command was already mentioned.  Two more statements can be used
+in between the ":while" and the ":endwhile":
+
+	:continue		Jump back to the start of the while loop; the
+				loop continues.
+	:break			Jump forward to the ":endwhile"; the loop is
+				discontinued.
+
+Example: >
+
+	:while counter < 40
+	:  call do_something()
+	:  if skip_flag
+	:    continue
+	:  endif
+	:  if finished_flag
+	:    break
+	:  endif
+	:  sleep 50m
+	:endwhile
+
+The ":sleep" command makes Vim take a nap.  The "50m" specifies fifty
+milliseconds.  Another example is ":sleep 4", which sleeps for four seconds.
+
+==============================================================================
+*41.5*	Executing an expression
+
+So far the commands in the script were executed by Vim directly.  The
+":execute" command allows executing the result of an expression.  This is a
+very powerful way to build commands and execute them.
+   An example is to jump to a tag, which is contained in a variable: >
+
+	:execute "tag " . tag_name
+
+The "." is used to concatenate the string "tag " with the value of variable
+"tag_name".  Suppose "tag_name" has the value "get_cmd", then the command that
+will be executed is: >
+
+	:tag get_cmd
+
+The ":execute" command can only execute colon commands.  The ":normal" command
+executes Normal mode commands.  However, its argument is not an expression but
+the literal command characters.  Example: >
+
+	:normal gg=G
+
+This jumps to the first line and formats all lines with the "=" operator.
+   To make ":normal" work with an expression, combine ":execute" with it.
+Example: >
+
+	:execute "normal " . normal_commands
+
+The variable "normal_commands" must contain the Normal mode commands.
+   Make sure that the argument for ":normal" is a complete command.  Otherwise
+Vim will run into the end of the argument and abort the command.  For example,
+if you start Insert mode, you must leave Insert mode as well.  This works: >
+
+	:execute "normal Inew text \<Esc>"
+
+This inserts "new text " in the current line.  Notice the use of the special
+key "\<Esc>".  This avoids having to enter a real <Esc> character in your
+script.
+
+==============================================================================
+*41.6*	Using functions
+
+Vim defines many functions and provides a large amount of functionality that
+way.  A few examples will be given in this section.  You can find the whole
+list here: |functions|.
+
+A function is called with the ":call" command.  The parameters are passed in
+between braces, separated by commas.  Example: >
+
+	:call search("Date: ", "W")
+
+This calls the search() function, with arguments "Date: " and "W".  The
+search() function uses its first argument as a search pattern and the second
+one as flags.  The "W" flag means the search doesn't wrap around the end of
+the file.
+
+A function can be called in an expression.  Example: >
+
+	:let line = getline(".")
+	:let repl = substitute(line, '\a', "*", "g")
+	:call setline(".", repl)
+
+The getline() function obtains a line from the current file.  Its argument is
+a specification of the line number.  In this case "." is used, which means the
+line where the cursor is.
+   The substitute() function does something similar to the ":substitute"
+command.  The first argument is the string on which to perform the
+substitution.  The second argument is the pattern, the third the replacement
+string.  Finally, the last arguments are the flags.
+   The setline() function sets the line, specified by the first argument, to a
+new string, the second argument.  In this example the line under the cursor is
+replaced with the result of the substitute().  Thus the effect of the three
+statements is equal to: >
+
+	:substitute/\a/*/g
+
+Using the functions becomes more interesting when you do more work before and
+after the substitute() call.
+
+
+FUNCTIONS						*function-list*
+
+There are many functions.  We will mention them here, grouped by what they are
+used for.  You can find an alphabetical list here: |functions|.  Use CTRL-] on
+the function name to jump to detailed help on it.
+
+String manipulation:
+	char2nr()		get ASCII value of a character
+	nr2char()		get a character by its ASCII value
+	escape()		escape characters in a string with a '\'
+	strtrans()		translate a string to make it printable
+	tolower()		turn a string to lowercase
+	toupper()		turn a string to uppercase
+	match()			position where a pattern matches in a string
+	matchend()		position where a pattern match ends in a string
+	matchstr()		match of a pattern in a string
+	stridx()		first index of a short string in a long string
+	strridx()		last index of a short string in a long string
+	strlen()		length of a string
+	substitute()		substitute a pattern match with a string
+	submatch()		get a specific match in a ":substitute"
+	strpart()		get part of a string
+	expand()		expand special keywords
+	type()			type of a variable
+	iconv()			convert text from one encoding to another
+
+Working with text in the current buffer:
+	byte2line()		get line number at a specific byte count
+	line2byte()		byte count at a specific line
+	col()			column number of the cursor or a mark
+	virtcol()		screen column of the cursor or a mark
+	line()			line number of the cursor or mark
+	wincol()		window column number of the cursor
+	winline()		window line number of the cursor
+	cursor()		position the cursor at a line/column
+	getline()		get a line from the buffer
+	setline()		replace a line in the buffer
+	append()		append {string} below line {lnum}
+	indent()		indent of a specific line
+	cindent()		indent according to C indenting
+	lispindent()		indent according to Lisp indenting
+	nextnonblank()		find next non-blank line
+	prevnonblank()		find previous non-blank line
+	search()		find a match for a pattern
+	searchpair()		find the other end of a start/skip/end
+
+System functions and manipulation of files:
+	browse()		put up a file requester
+	glob()			expand wildcards
+	globpath()		expand wildcards in a number of directories
+	resolve()		find out where a shortcut points to
+	fnamemodify()		modify a file name
+	executable()		check if an executable program exists
+	filereadable()		check if a file can be read
+	filewritable()		check if a file can be written to
+	isdirectory()		check if a directory exists
+	getcwd()		get the current working directory
+	getfsize()		get the size of a file
+	getftime()		get last modification time of a file
+	localtime()		get current time
+	strftime()		convert time to a string
+	tempname()		get the name of a temporary file
+	delete()		delete a file
+	rename()		rename a file
+	system()		get the result of a shell command
+	hostname()		name of the system
+
+Buffers, windows and the argument list:
+	argc()			number of entries in the argument list
+	argidx()		current position in the argument list
+	argv()			get one entry from the argument list
+	bufexists()		check if a buffer exists
+	buflisted()		check if a buffer exists and is listed
+	bufloaded()		check if a buffer exists and is loaded
+	bufname()		get the name of a specific buffer
+	bufnr()			get the buffer number of a specific buffer
+	winnr()			get the window number for the current window
+	bufwinnr()		get the window number of a specific buffer
+	winbufnr()		get the buffer number of a specific window
+	getbufvar()		get a variable value from a specific buffer
+	setbufvar()		set a variable in a specific buffer
+	getwinvar()		get a variable value from a specific window
+	setwinvar()		set a variable in a specific window
+
+Folding:
+	foldclosed()		check for a closed fold at a specific line
+	foldclosedend()		like foldclosed() but return the last line
+	foldlevel()		check for the fold level at a specific line
+	foldtext()		generate the line displayed for a closed fold
+
+Syntax highlighting:
+	hlexists()		check if a highlight group exists
+	hlID()			get ID of a highlight group
+	synID()			get syntax ID at a specific position
+	synIDattr()		get a specific attribute of a syntax ID
+	synIDtrans()		get translated syntax ID
+
+History:
+	histadd()		add an item to a history
+	histdel()		delete an item from a history
+	histget()		get an item from a history
+	histnr()		get highest index of a history list
+
+Interactive:
+	confirm()		let the user make a choice
+	getchar()		get a character from the user
+	getcharmod()		get modifiers for the last typed character
+	input()			get a line from the user
+	inputsecret()		get a line from the user without showing it
+	inputdialog()		get a line from the user in a dialog
+	inputresave		save and clear typeahead
+	inputrestore()		restore typeahead
+
+Vim server:
+	serverlist()		return the list of server names
+	remote_send()		send command characters to a Vim server
+	remote_expr()		evaluate an expression in a Vim server
+	server2client()		send a reply to a client of a Vim server
+	remote_peek()		check if there is a reply from a Vim server
+	remote_read()		read a reply from a Vim server
+	foreground()		move the Vim window to the foreground
+	remote_foreground()	move the Vim server window to the foreground
+
+Various:
+	mode()			get current editing mode
+	visualmode()		last visual mode used
+	hasmapto()		check if a mapping exists
+	mapcheck()		check if a matching mapping exists
+	maparg()		get rhs of a mapping
+	exists()		check if a variable, function, etc. exists
+	has()			check if a feature is supported in Vim
+	cscope_connection()	check if a cscope connection exists
+	did_filetype()		check if a FileType autocommand was used
+	eventhandler()		check if invoked by an event handler
+	getwinposx()		X position of the GUI Vim window
+	getwinposy()		Y position of the GUI Vim window
+	winheight()		get height of a specific window
+	winwidth()		get width of a specific window
+	libcall()		call a function in an external library
+	libcallnr()		idem, returning a number
+	getreg()		get contents of a register
+	getregtype()		get type of a register
+	setreg()		set contents and type of a register
+
+==============================================================================
+*41.7*	Defining a function
+
+Vim enables you to define your own functions.  The basic function declaration
+begins as follows: >
+
+	:function {name}({var1}, {var2}, ...)
+	:  {body}
+	:endfunction
+<
+	Note:
+	Function names must begin with a capital letter.
+
+Let's define a short function to return the smaller of two numbers.  It starts
+with this line: >
+
+	:function Min(num1, num2)
+
+This tells Vim that the function is named "Min" and it takes two arguments:
+"num1" and "num2".
+   The first thing you need to do is to check to see which number is smaller:
+   >
+	:  if a:num1 < a:num2
+
+The special prefix "a:" tells Vim that the variable is a function argument.
+Let's assign the variable "smaller" the value of the smallest number: >
+
+	:  if a:num1 < a:num2
+	:    let smaller = a:num1
+	:  else
+	:    let smaller = a:num2
+	:  endif
+
+The variable "smaller" is a local variable.  Variables used inside a function
+are local unless prefixed by something like "g:", "a:", or "s:".
+
+	Note:
+	To access a global variable from inside a function you must prepend
+	"g:" to it.  Thus "g:count" inside a function is used for the global
+	variable "count", and "count" is another variable, local to the
+	function.
+
+You now use the ":return" statement to return the smallest number to the user.
+Finally, you end the function: >
+
+	:  return smaller
+	:endfunction
+
+The complete function definition is as follows: >
+
+	:function Min(num1, num2)
+	:  if a:num1 < a:num2
+	:    let smaller = a:num1
+	:  else
+	:    let smaller = a:num2
+	:  endif
+	:  return smaller
+	:endfunction
+
+A user defined function is called in exactly the same way as a builtin
+function.  Only the name is different.  The Min function can be used like
+this: >
+
+	:echo Min(5, 8)
+
+Only now will the function be executed and the lines be interpreted by Vim.
+If there are mistakes, like using an undefined variable or function, you will
+now get an error message.  When defining the function these errors are not
+detected.
+
+When a function reaches ":endfunction" or ":return" is used without an
+argument, the function returns zero.
+
+To redefine a function that already exists, use the ! for the ":function"
+command: >
+
+	:function!  Min(num1, num2, num3)
+
+
+USING A RANGE
+
+The ":call" command can be given a line range.  This can have one of two
+meanings.  When a function has been defined with the "range" keyword, it will
+take care of the line range itself.
+  The function will be passed the variables "a:firstline" and "a:lastline".
+These will have the line numbers from the range the function was called with.
+Example: >
+
+	:function Count_words() range
+	:  let n = a:firstline
+	:  let count = 0
+	:  while n <= a:lastline
+	:    let count = count + Wordcount(getline(n))
+	:    let n = n + 1
+	:  endwhile
+	:  echo "found " . count . " words"
+	:endfunction
+
+You can call this function with: >
+
+	:10,30call Count_words()
+
+It will be executed once and echo the number of words.
+   The other way to use a line range is by defining a function without the
+"range" keyword.  The function will be called once for every line in the
+range, with the cursor in that line.  Example: >
+
+	:function  Number()
+	:  echo "line " . line(".") . " contains: " . getline(".")
+	:endfunction
+
+If you call this function with: >
+
+	:10,15call Number()
+
+The function will be called six times.
+
+
+VARIABLE NUMBER OF ARGUMENTS
+
+Vim enables you to define functions that have a variable number of arguments.
+The following command, for instance, defines a function that must have 1
+argument (start) and can have up to 20 additional arguments: >
+
+	:function Show(start, ...)
+
+The variable "a:1" contains the first optional argument, "a:2" the second, and
+so on.  The variable "a:0" contains the number of extra arguments.
+   For example: >
+
+	:function Show(start, ...)
+	:  echohl Title
+	:  echo "Show is " . a:start
+	:  echohl None
+	:  let index = 1
+	:  while index <= a:0
+	:    echo "  Arg " . index . " is " . a:{index}
+	:    let index = index + 1
+	:  endwhile
+	:  echo ""
+	:endfunction
+
+This uses the ":echohl" command to specify the highlighting used for the
+following ":echo" command.  ":echohl None" stops it again.  The ":echon"
+command works like ":echo", but doesn't output a line break.
+
+
+LISTING FUNCTIONS
+
+The ":function" command lists the names and arguments of all user-defined
+functions: >
+
+	:function
+<	function Show(start, ...) ~
+	function GetVimIndent() ~
+	function SetSyn(name) ~
+
+To see what a function does, use its name as an argument for ":function": >
+
+	:function SetSyn
+<	1     if &syntax == '' ~
+	2       let &syntax = a:name ~
+	3     endif ~
+	   endfunction ~
+
+
+DEBUGGING
+
+The line number is useful for when you get an error message or when debugging.
+See |debug-scripts| about debugging mode.
+   You can also set the 'verbose' option to 12 or higher to see all function
+calls.  Set it to 15 or higher to see every executed line.
+
+
+DELETING A FUNCTION
+
+To delete the Show() function: >
+
+	:delfunction Show
+
+You get an error when the function doesn't exist.
+
+==============================================================================
+*41.8*	Exceptions
+
+Let's start with an example: >
+
+	:try
+	:   read ~/templates/pascal.tmpl
+	:catch /E484:/
+	:   echo "Sorry, the Pascal template file cannot be found."
+	:endtry
+
+The ":read" command will fail if the file does not exist.  Instead of
+generating an error message, this code catches the error and gives the user a
+nice message instead.
+
+For the commands in between ":try" and ":endtry" errors are turned into
+exceptions.  An exception is a string.  In the case of an error the string
+contains the error message.  And every error message has a number.  In this
+case, the error we catch contains "E484:".  This number is guaranteed to stay
+the same (the text may change, e.g., it may be translated).
+
+When the ":read" command causes another error, the pattern "E484:" will not
+match in it.  Thus this exception will not be caught and result in the usual
+error message.
+
+You might be tempted to do this: >
+
+	:try
+	:   read ~/templates/pascal.tmpl
+	:catch
+	:   echo "Sorry, the Pascal template file cannot be found."
+	:endtry
+
+This means all errors are caught.  But then you will not see errors that are
+useful, such as "E21: Cannot make changes, 'modifiable' is off".
+
+Another useful mechanism is the ":finally" command: >
+
+	:let tmp = tempname()
+	:try
+	:   exe ".,$write " . tmp
+	:   exe "!filter " . tmp
+	:   .,$delete
+	:   exe "$read " . tmp
+	:finally
+	:   call delete(tmp)
+	:endtry
+
+This filters the lines from the cursor until the end of the file through the
+"filter" command, which takes a file name argument.  No matter if the
+filtering works, something goes wrong in between ":try" and ":finally" or the
+user cancels the filtering by pressing CTRL-C, the "call delete(tmp)" is
+always executed.  This makes sure you don't leave the temporary file behind.
+
+More information about exception handling can be found in the reference
+manual: |exception-handling|.
+
+==============================================================================
+*41.9*	Various remarks
+
+Here is a summary of items that apply to Vim scripts.  They are also mentioned
+elsewhere, but form a nice checklist.
+
+The end-of-line character depends on the system.  For Unix a single <NL>
+character is used.  For MS-DOS, Windows, OS/2 and the like, <CR><LF> is used.
+This is important when using mappings that end in a <CR>.  See |:source_crnl|.
+
+
+WHITE SPACE
+
+Blank lines are allowed and ignored.
+
+Leading whitespace characters (blanks and TABs) are always ignored.  The
+whitespaces between parameters (e.g. between the 'set' and the 'cpoptions' in
+the example below) are reduced to one blank character and plays the role of a
+separator, the whitespaces after the last (visible) character may or may not
+be ignored depending on the situation, see below.
+
+For a ":set" command involving the "=" (equal) sign, such as in: >
+
+	:set cpoptions    =aABceFst
+
+the whitespace immediately before the "=" sign is ignored.  But there can be
+no whitespace after the "=" sign!
+
+To include a whitespace character in the value of an option, it must be
+escaped by a "\" (backslash)  as in the following example: >
+
+	:set tags=my\ nice\ file
+
+The same example written as >
+
+	:set tags=my nice file
+
+will issue an error, because it is interpreted as: >
+
+	:set tags=my
+	:set nice
+	:set file
+
+
+COMMENTS
+
+The character " (the double quote mark) starts a comment.  Everything after
+and including this character until the end-of-line is considered a comment and
+is ignored, except for commands that don't consider comments, as shown in
+examples below.  A comment can start on any character position on the line.
+
+There is a little "catch" with comments for some commands.  Examples: >
+
+	:abbrev dev development		" shorthand
+	:map <F3> o#include		" insert include
+	:execute cmd			" do it
+	:!ls *.c			" list C files
+
+The abbreviation 'dev' will be expanded to 'development     " shorthand'.  The
+mapping of <F3> will actually be the whole line after the 'o# ....' including
+the '" insert include'.  The "execute" command will give an error.  The "!"
+command will send everything after it to the shell, causing an error for an
+unmatched '"' character.
+   There can be no comment after ":map", ":abbreviate", ":execute" and "!"
+commands (there are a few more commands with this restriction).  For the
+":map", ":abbreviate" and ":execute" commands there is a trick: >
+
+	:abbrev dev development|" shorthand
+	:map <F3> o#include|" insert include
+	:execute cmd			|" do it
+
+With the '|' character the command is separated from the next one.  And that
+next command is only a comment.
+
+Notice that there is no white space before the '|' in the abbreviation and
+mapping.  For these commands, any character until the end-of-line or '|' is
+included.  As a consequence of this behavior, you don't always see that
+trailing whitespace is included: >
+
+	:map <F4> o#include  
+
+To avoid these problems, you can set the 'list' option when editing vimrc
+files.
+
+
+PITFALLS
+
+Even bigger problem arises in the following example: >
+
+	:map ,ab o#include
+	:unmap ,ab 
+
+Here the unmap command will not work, because it tries to unmap ",ab ".  This
+does not exist as a mapped sequence.  An error will be issued, which is very
+hard to identify, because the ending whitespace character in ":unmap ,ab " is
+not visible.
+
+And this is the same as what happens when one uses a comment after an 'unmap'
+command: >
+
+	:unmap ,ab     " comment
+
+Here the comment part will be ignored.  However, Vim will try to unmap
+',ab     ', which does not exist.  Rewrite it as: >
+
+	:unmap ,ab|    " comment
+
+
+RESTORING THE VIEW
+
+Sometimes you want to make a change and go back to where cursor was.
+Restoring the relative position would also be nice, so that the same line
+appears at the top of the window.
+   This example yanks the current line, puts it above the first line in the
+file and then restores the view: >
+
+	map ,p ma"aYHmbgg"aP`bzt`a
+
+What this does: >
+	ma"aYHmbgg"aP`bzt`a
+<	ma			set mark a at cursor position
+	  "aY			yank current line into register a
+	     Hmb		go to top line in window and set mark b there
+		gg		go to first line in file
+		  "aP		put the yanked line above it
+		     `b		go back to top line in display
+		       zt	position the text in the window as before
+			 `a	go back to saved cursor position
+
+
+PACKAGING
+
+To avoid your function names to interfere with functions that you get from
+others, use this scheme:
+- Prepend a unique string before each function name.  I often use an
+  abbreviation.  For example, "OW_" is used for the option window functions.
+- Put the definition of your functions together in a file.  Set a global
+  variable to indicate that the functions have been loaded.  When sourcing the
+  file again, first unload the functions.
+Example: >
+
+	" This is the XXX package
+
+	if exists("XXX_loaded")
+	  delfun XXX_one
+	  delfun XXX_two
+	endif
+
+	function XXX_one(a)
+		... body of function ...
+	endfun
+
+	function XXX_two(b)
+		... body of function ...
+	endfun
+
+	let XXX_loaded = 1
+
+==============================================================================
+*41.10*	Writing a plugin				*write-plugin*
+
+You can write a Vim script in such a way that many people can use it.  This is
+called a plugin.  Vim users can drop your script in their plugin directory and
+use its features right away |add-plugin|.
+
+There are actually two types of plugins:
+
+  global plugins: For all types of files.
+filetype plugins: Only for files of a specific type.
+
+In this section the first type is explained.  Most items are also relevant for
+writing filetype plugins.  The specifics for filetype plugins are in the next
+section |write-filetype-plugin|.
+
+
+NAME
+
+First of all you must choose a name for your plugin.  The features provided
+by the plugin should be clear from its name.  And it should be unlikely that
+someone else writes a plugin with the same name but which does something
+different.  And please limit the name to 8 characters, to avoid problems on
+old Windows systems.
+
+A script that corrects typing mistakes could be called "typecorr.vim".  We
+will use it here as an example.
+
+For the plugin to work for everybody, it should follow a few guidelines.  This
+will be explained step-by-step.  The complete example plugin is at the end.
+
+
+BODY
+
+Let's start with the body of the plugin, the lines that do the actual work: >
+
+ 14	iabbrev teh the
+ 15	iabbrev otehr other
+ 16	iabbrev wnat want
+ 17	iabbrev synchronisation
+ 18		\ synchronization
+ 19	let s:count = 4
+
+The actual list should be much longer, of course.
+
+The line numbers have only been added to explain a few things, don't put them
+in your plugin file!
+
+
+HEADER
+
+You will probably add new corrections to the plugin and soon have several
+versions laying around.  And when distributing this file, people will want to
+know who wrote this wonderful plugin and where they can send remarks.
+Therefore, put a header at the top of your plugin: >
+
+  1	" Vim global plugin for correcting typing mistakes
+  2	" Last Change:	2000 Oct 15
+  3	" Maintainer:	Bram Moolenaar <Bram@vim.org>
+
+About copyright and licensing: Since plugins are very useful and it's hardly
+worth restricting their distribution, please consider making your plugin
+either public domain or use the Vim |license|.  A short note about this near
+the top of the plugin should be sufficient.  Example: >
+
+  4	" License:	This file is placed in the public domain.
+
+
+LINE CONTINUATION, AVOIDING SIDE EFFECTS		*use-cpo-save*
+
+In line 18 above, the line-continuation mechanism is used |line-continuation|.
+Users with 'compatible' set will run into trouble here, they will get an error
+message.  We can't just reset 'compatible', because that has a lot of side
+effects.  To avoid this, we will set the 'cpoptions' option to its Vim default
+value and restore it later.  That will allow the use of line-continuation and
+make the script work for most people.  It is done like this: >
+
+ 11	let s:save_cpo = &cpo
+ 12	set cpo&vim
+ ..
+ 42	let &cpo = s:save_cpo
+
+We first store the old value of 'cpoptions' in the s:save_cpo variable.  At
+the end of the plugin this value is restored.
+
+Notice that a script-local variable is used |s:var|.  A global variable could
+already be in use for something else.  Always use script-local variables for
+things that are only used in the script.
+
+
+NOT LOADING
+
+It's possible that a user doesn't always want to load this plugin.  Or the
+system administrator has dropped it in the system-wide plugin directory, but a
+user has his own plugin he wants to use.  Then the user must have a chance to
+disable loading this specific plugin.  This will make it possible: >
+
+  6	if exists("loaded_typecorr")
+  7	  finish
+  8	endif
+  9	let loaded_typecorr = 1
+
+This also avoids that when the script is loaded twice it would cause error
+messages for redefining functions and cause trouble for autocommands that are
+added twice.
+
+
+MAPPING
+
+Now let's make the plugin more interesting: We will add a mapping that adds a
+correction for the word under the cursor.  We could just pick a key sequence
+for this mapping, but the user might already use it for something else.  To
+allow the user to define which keys a mapping in a plugin uses, the <Leader>
+item can be used: >
+
+ 22	  map <unique> <Leader>a  <Plug>TypecorrAdd
+
+The "<Plug>TypecorrAdd" thing will do the work, more about that further on.
+
+The user can set the "mapleader" variable to the key sequence that he wants
+this mapping to start with.  Thus if the user has done: >
+
+	let mapleader = "_"
+
+the mapping will define "_a".  If the user didn't do this, the default value
+will be used, which is a backslash.  Then a map for "\a" will be defined.
+
+Note that <unique> is used, this will cause an error message if the mapping
+already happened to exist. |:map-<unique>|
+
+But what if the user wants to define his own key sequence?  We can allow that
+with this mechanism: >
+
+ 21	if !hasmapto('<Plug>TypecorrAdd')
+ 22	  map <unique> <Leader>a  <Plug>TypecorrAdd
+ 23	endif
+
+This checks if a mapping to "<Plug>TypecorrAdd" already exists, and only
+defines the mapping from "<Leader>a" if it doesn't.  The user then has a
+chance of putting this in his vimrc file: >
+
+	map ,c  <Plug>TypecorrAdd
+
+Then the mapped key sequence will be ",c" instead of "_a" or "\a".
+
+
+PIECES
+
+If a script gets longer, you often want to break up the work in pieces.  You
+can use functions or mappings for this.  But you don't want these functions
+and mappings to interfere with the ones from other scripts.  For example, you
+could define a function Add(), but another script could try to define the same
+function.  To avoid this, we define the function local to the script by
+prepending it with "s:".
+
+We will define a function that adds a new typing correction: >
+
+ 30	function s:Add(from, correct)
+ 31	  let to = input("type the correction for " . a:from . ": ")
+ 32	  exe ":iabbrev " . a:from . " " . to
+ ..
+ 36	endfunction
+
+Now we can call the function s:Add() from within this script.  If another
+script also defines s:Add(), it will be local to that script and can only
+be called from the script it was defined in.  There can also be a global Add()
+function (without the "s:"), which is again another function.
+
+<SID> can be used with mappings.  It generates a script ID, which identifies
+the current script.  In our typing correction plugin we use it like this: >
+
+ 24	noremap <unique> <script> <Plug>TypecorrAdd  <SID>Add
+ ..
+ 28	noremap <SID>Add  :call <SID>Add(expand("<cword>"), 1)<CR>
+
+Thus when a user types "\a", this sequence is invoked: >
+
+	\a  ->  <Plug>TypecorrAdd  ->  <SID>Add  ->  :call <SID>Add()
+
+If another script would also map <SID>Add, it would get another script ID and
+thus define another mapping.
+
+Note that instead of s:Add() we use <SID>Add() here.  That is because the
+mapping is typed by the user, thus outside of the script.  The <SID> is
+translated to the script ID, so that Vim knows in which script to look for
+the Add() function.
+
+This is a bit complicated, but it's required for the plugin to work together
+with other plugins.  The basic rule is that you use <SID>Add() in mappings and
+s:Add() in other places (the script itself, autocommands, user commands).
+
+We can also add a menu entry to do the same as the mapping: >
+
+ 26	noremenu <script> Plugin.Add\ Correction      <SID>Add
+
+The "Plugin" menu is recommended for adding menu items for plugins.  In this
+case only one item is used.  When adding more items, creating a submenu is
+recommended.  For example, "Plugin.CVS" could be used for a plugin that offers
+CVS operations "Plugin.CVS.checkin", "Plugin.CVS.checkout", etc.
+
+Note that in line 28 ":noremap" is used to avoid that any other mappings cause
+trouble.  Someone may have remapped ":call", for example.  In line 24 we also
+use ":noremap", but we do want "<SID>Add" to be remapped.  This is why
+"<script>" is used here.  This only allows mappings which are local to the
+script. |:map-<script>|  The same is done in line 26 for ":noremenu".
+|:menu-<script>|
+
+
+<SID> AND <Plug>					*using-<Plug>*
+
+Both <SID> and <Plug> are used to avoid that mappings of typed keys interfere
+with mappings that are only to be used from other mappings.  Note the
+difference between using <SID> and <Plug>:
+
+<Plug>	is visible outside of the script.  It is used for mappings which the
+	user might want to map a key sequence to.  <Plug> is a special code
+	that a typed key will never produce.
+	To make it very unlikely that other plugins use the same sequence of
+	characters, use this structure: <Plug> scriptname mapname
+	In our example the scriptname is "Typecorr" and the mapname is "Add".
+	This results in "<Plug>TypecorrAdd".  Only the first character of
+	scriptname and mapname is uppercase, so that we can see where mapname
+	starts.
+
+<SID>	is the script ID, a unique identifier for a script.
+	Internally Vim translates <SID> to "<SNR>123_", where "123" can be any
+	number.  Thus a function "<SID>Add()" will have a name "<SNR>11_Add()"
+	in one script, and "<SNR>22_Add()" in another.  You can see this if
+	you use the ":function" command to get a list of functions.  The
+	translation of <SID> in mappings is exactly the same, that's how you
+	can call a script-local function from a mapping.
+
+
+USER COMMAND
+
+Now let's add a user command to add a correction: >
+
+ 38	if !exists(":Correct")
+ 39	  command -nargs=1  Correct  :call s:Add(<q-args>, 0)
+ 40	endif
+
+The user command is defined only if no command with the same name already
+exists.  Otherwise we would get an error here.  Overriding the existing user
+command with ":command!" is not a good idea, this would probably make the user
+wonder why the command he defined himself doesn't work.  |:command|
+
+
+SCRIPT VARIABLES
+
+When a variable starts with "s:" it is a script variable.  It can only be used
+inside a script.  Outside the script it's not visible.  This avoids trouble
+with using the same variable name in different scripts.  The variables will be
+kept as long as Vim is running.  And the same variables are used when sourcing
+the same script again. |s:var|
+
+The fun is that these variables can also be used in functions, autocommands
+and user commands that are defined in the script.  In our example we can add
+a few lines to count the number of corrections: >
+
+ 19	let s:count = 4
+ ..
+ 30	function s:Add(from, correct)
+ ..
+ 34	  let s:count = s:count + 1
+ 35	  echo s:count . " corrections now"
+ 36	endfunction
+
+First s:count is initialized to 4 in the script itself.  When later the
+s:Add() function is called, it increments s:count.  It doesn't matter from
+where the function was called, since it has been defined in the script, it
+will use the local variables from this script.
+
+
+THE RESULT
+
+Here is the resulting complete example: >
+
+  1	" Vim global plugin for correcting typing mistakes
+  2	" Last Change:	2000 Oct 15
+  3	" Maintainer:	Bram Moolenaar <Bram@vim.org>
+  4	" License:	This file is placed in the public domain.
+  5
+  6	if exists("loaded_typecorr")
+  7	  finish
+  8	endif
+  9	let loaded_typecorr = 1
+ 10
+ 11	let s:save_cpo = &cpo
+ 12	set cpo&vim
+ 13
+ 14	iabbrev teh the
+ 15	iabbrev otehr other
+ 16	iabbrev wnat want
+ 17	iabbrev synchronisation
+ 18		\ synchronization
+ 19	let s:count = 4
+ 20
+ 21	if !hasmapto('<Plug>TypecorrAdd')
+ 22	  map <unique> <Leader>a  <Plug>TypecorrAdd
+ 23	endif
+ 24	noremap <unique> <script> <Plug>TypecorrAdd  <SID>Add
+ 25
+ 26	noremenu <script> Plugin.Add\ Correction      <SID>Add
+ 27
+ 28	noremap <SID>Add  :call <SID>Add(expand("<cword>"), 1)<CR>
+ 29
+ 30	function s:Add(from, correct)
+ 31	  let to = input("type the correction for " . a:from . ": ")
+ 32	  exe ":iabbrev " . a:from . " " . to
+ 33	  if a:correct | exe "normal viws\<C-R>\" \b\e" | endif
+ 34	  let s:count = s:count + 1
+ 35	  echo s:count . " corrections now"
+ 36	endfunction
+ 37
+ 38	if !exists(":Correct")
+ 39	  command -nargs=1  Correct  :call s:Add(<q-args>, 0)
+ 40	endif
+ 41
+ 42	let &cpo = s:save_cpo
+
+Line 33 wasn't explained yet.  It applies the new correction to the word under
+the cursor.  The |:normal| command is used to use the new abbreviation.  Note
+that mappings and abbreviations are expanded here, even though the function
+was called from a mapping defined with ":noremap".
+
+Using "unix" for the 'fileformat' option is recommended.  The Vim scripts will
+then work everywhere.  Scripts with 'fileformat' set to "dos" do not work on
+Unix.  Also see |:source_crnl|.  To be sure it is set right, do this before
+writing the file: >
+
+	:set fileformat=unix
+
+
+DOCUMENTATION						*write-local-help*
+
+It's a good idea to also write some documentation for your plugin.  Especially
+when its behavior can be changed by the user.  See |add-local-help| for how
+they are installed.
+
+Here is a simple example for a plugin help file, called "typecorr.txt": >
+
+  1	*typecorr.txt*	Plugin for correcting typing mistakes
+  2
+  3	If you make typing mistakes, this plugin will have them corrected
+  4	automatically.
+  5
+  6	There are currently only a few corrections.  Add your own if you like.
+  7
+  8	Mappings:
+  9	<Leader>a   or   <Plug>TypecorrAdd
+ 10		Add a correction for the word under the cursor.
+ 11
+ 12	Commands:
+ 13	:Correct {word}
+ 14		Add a correction for {word}.
+ 15
+ 16							*typecorr-settings*
+ 17	This plugin doesn't have any settings.
+
+The first line is actually the only one for which the format matters.  It will
+be extracted from the help file to be put in the "LOCAL ADDITIONS:" section of
+help.txt |local-additions|.  The first "*" must be in the first column of the
+first line.  After adding your help file do ":help" and check that the entries
+line up nicely.
+
+You can add more tags inside ** in your help file.  But be careful not to use
+existing help tags.  You would probably use the name of your plugin in most of
+them, like "typecorr-settings" in the example.
+
+Using references to other parts of the help in || is recommended.  This makes
+it easy for the user to find associated help.
+
+
+FILETYPE DETECTION					*plugin-filetype*
+
+If your filetype is not already detected by Vim, you should create a filetype
+detection snippet in a separate file.  It is usually in the form of an
+autocommand that sets the filetype when the file name matches a pattern.
+Example: >
+
+	au BufNewFile,BufRead *.foo			set filetype=foofoo
+
+Write this single-line file as "ftdetect/foofoo.vim" in the first directory
+that appears in 'runtimepath'.  For Unix that would be
+"~/.vim/ftdetect/foofoo.vim".  The convention is to use the name of the
+filetype for the script name.
+
+You can make more complicated checks if you like, for example to inspect the
+contents of the file to recognize the language.  Also see |new-filetype|.
+
+
+SUMMARY							*plugin-special*
+
+Summary of special things to use in a plugin:
+
+s:name			Variables local to the script.
+
+<SID>			Script-ID, used for mappings and functions local to
+			the script.
+
+hasmapto()		Function to test if the user already defined a mapping
+			for functionality the script offers.
+
+<Leader>		Value of "mapleader", which the user defines as the
+			keys that plugin mappings start with.
+
+:map <unique>		Give a warning if a mapping already exists.
+
+:noremap <script>	Use only mappings local to the script, not global
+			mappings.
+
+exists(":Cmd")		Check if a user command already exists.
+
+==============================================================================
+*41.11*	Writing a filetype plugin	*write-filetype-plugin* *ftplugin*
+
+A filetype plugin is like a global plugin, except that it sets options and
+defines mappings for the current buffer only.  See |add-filetype-plugin| for
+how this type of plugin is used.
+
+First read the section on global plugins above |41.10|.  All that is said there
+also applies to filetype plugins.  There are a few extras, which are explained
+here.  The essential thing is that a filetype plugin should only have an
+effect on the current buffer.
+
+
+DISABLING
+
+If you are writing a filetype plugin to be used by many people, they need a
+chance to disable loading it.  Put this at the top of the plugin: >
+
+	" Only do this when not done yet for this buffer
+	if exists("b:did_ftplugin")
+	  finish
+	endif
+	let b:did_ftplugin = 1
+
+This also needs to be used to avoid that the same plugin is executed twice for
+the same buffer (happens when using an ":edit" command without arguments).
+
+Now users can disable loading the default plugin completely by making a
+filetype plugin with only this line: >
+
+	let b:did_ftplugin = 1
+
+This does require that the filetype plugin directory comes before $VIMRUNTIME
+in 'runtimepath'!
+
+If you do want to use the default plugin, but overrule one of the settings,
+you can write the different setting in a script: >
+
+	setlocal textwidth=70
+
+Now write this in the "after" directory, so that it gets sourced after the
+distributed "vim.vim" ftplugin |after-directory|.  For Unix this would be
+"~/.vim/after/ftplugin/vim.vim".  Note that the default plugin will have set
+"b:did_ftplugin", but it is ignored here.
+
+
+OPTIONS
+
+To make sure the filetype plugin only affects the current buffer use the >
+
+	:setlocal
+
+command to set options.  And only set options which are local to a buffer (see
+the help for the option to check that).  When using |:setlocal| for global
+options or options local to a window, the value will change for many buffers,
+and that is not what a filetype plugin should do.
+
+When an option has a value that is a list of flags or items, consider using
+"+=" and "-=" to keep the existing value.  Be aware that the user may have
+changed an option value already.  First resetting to the default value and
+then changing it often a good idea.  Example: >
+
+	:setlocal formatoptions& formatoptions+=ro
+
+
+MAPPINGS
+
+To make sure mappings will only work in the current buffer use the >
+
+	:map <buffer>
+
+command.  This needs to be combined with the two-step mapping explained above.
+An example of how to define functionality in a filetype plugin: >
+
+	if !hasmapto('<Plug>JavaImport')
+	  map <buffer> <unique> <LocalLeader>i <Plug>JavaImport
+	endif
+	noremap <buffer> <unique> <Plug>JavaImport oimport ""<Left><Esc>
+
+|hasmapto()| is used to check if the user has already defined a map to
+<Plug>JavaImport.  If not, then the filetype plugin defines the default
+mapping.  This starts with |<LocalLeader>|, which allows the user to select
+the key(s) he wants filetype plugin mappings to start with.  The default is a
+backslash.
+"<unique>" is used to give an error message if the mapping already exists or
+overlaps with an existing mapping.
+|:noremap| is used to avoid that any other mappings that the user has defined
+interferes.  You might want to use ":noremap <script>" to allow remapping
+mappings defined in this script that start with <SID>.
+
+The user must have a chance to disable the mappings in a filetype plugin,
+without disabling everything.  Here is an example of how this is done for a
+plugin for the mail filetype: >
+
+	" Add mappings, unless the user didn't want this.
+	if !exists("no_plugin_maps") && !exists("no_mail_maps")
+	  " Quote text by inserting "> "
+	  if !hasmapto('<Plug>MailQuote')
+	    vmap <buffer> <LocalLeader>q <Plug>MailQuote
+	    nmap <buffer> <LocalLeader>q <Plug>MailQuote
+	  endif
+	  vnoremap <buffer> <Plug>MailQuote :s/^/> /<CR>
+	  nnoremap <buffer> <Plug>MailQuote :.,$s/^/> /<CR>
+	endif
+
+Two global variables are used:
+no_plugin_maps		disables mappings for all filetype plugins
+no_mail_maps		disables mappings for a specific filetype
+
+
+USER COMMANDS
+
+To add a user command for a specific file type, so that it can only be used in
+one buffer, use the "-buffer" argument to |:command|.  Example: >
+
+	:command -buffer  Make  make %:r.s
+
+
+VARIABLES
+
+A filetype plugin will be sourced for each buffer of the type it's for.  Local
+script variables |s:var| will be shared between all invocations.  Use local
+buffer variables |b:var| if you want a variable specifically for one buffer.
+
+
+FUNCTIONS
+
+When defining a function, this only needs to be done once.  But the filetype
+plugin will be sourced every time a file with this filetype will be opened.
+This construct make sure the function is only defined once: >
+
+	:if !exists("*s:Func")
+	:  function s:Func(arg)
+	:    ...
+	:  endfunction
+	:endif
+<
+
+UNDO							*undo_ftplugin*
+
+When the user does ":setfiletype xyz" the effect of the previous filetype
+should be undone.  Set the b:undo_ftplugin variable to the commands that will
+undo the settings in your filetype plugin.  Example: >
+
+	let b:undo_ftplugin = "setlocal fo< com< tw< commentstring<"
+		\ . "| unlet b:match_ignorecase b:match_words b:match_skip"
+
+Using ":setlocal" with "<" after the option name resets the option to its
+global value.  That is mostly the best way to reset the option value.
+
+This does require removing the "C" flag from 'cpoptions' to allow line
+continuation, as mentioned above |use-cpo-save|.
+
+
+FILE NAME
+
+The filetype must be included in the file name |ftplugin-name|.  Use one of
+these three forms:
+
+	.../ftplugin/stuff.vim
+	.../ftplugin/stuff_foo.vim
+	.../ftplugin/stuff/bar.vim
+
+"stuff" is the filetype, "foo" and "bar" are arbitrary names.
+
+
+SUMMARY							*ftplugin-special*
+
+Summary of special things to use in a filetype plugin:
+
+<LocalLeader>		Value of "maplocalleader", which the user defines as
+			the keys that filetype plugin mappings start with.
+
+:map <buffer>		Define a mapping local to the buffer.
+
+:noremap <script>	Only remap mappings defined in this script that start
+			with <SID>.
+
+:setlocal		Set an option for the current buffer only.
+
+:command -buffer	Define a user command local to the buffer.
+
+exists("*s:Func")	Check if a function was already defined.
+
+Also see |plugin-special|, the special things used for all plugins.
+
+==============================================================================
+*41.12*	Writing a compiler plugin		*write-compiler-plugin*
+
+A compiler plugin sets options for use with a specific compiler.  The user can
+load it with the |:compiler| command.  The main use is to set the
+'errorformat' and 'makeprg' options.
+
+Easiest is to have a look at examples.  This command will edit all the default
+compiler plugins: >
+
+	:next $VIMRUNTIME/compiler/*.vim
+
+Use |:next| to go to the next plugin file.
+
+There are two special items about these files.  First is a mechanism to allow
+a user to overrule or add to the default file.  The default files start with: >
+
+	:if exists("current_compiler")
+	:  finish
+	:endif
+	:let current_compiler = "mine"
+
+When you write a compiler file and put it in your personal runtime directory
+(e.g., ~/.vim/compiler for Unix), you set the "current_compiler" variable to
+make the default file skip the settings.
+
+The second mechanism is to use ":set" for ":compiler!" and ":setlocal" for
+":compiler".  Vim defines the ":CompilerSet" user command for this.  However,
+older Vim versions don't, thus your plugin should define it then.  This is an
+example: >
+
+  if exists(":CompilerSet") != 2
+    command -nargs=* CompilerSet setlocal <args>
+  endif
+  CompilerSet errorformat&		" use the default 'errorformat'
+  CompilerSet makeprg=nmake
+
+When you write a compiler plugin for the Vim distribution or for a system-wide
+runtime directory, use the mechanism mentioned above.  When
+"current_compiler" was already set by a user plugin nothing will be done.
+
+When you write a compiler plugin to overrule settings from a default plugin,
+don't check "current_compiler".  This plugin is supposed to be loaded
+last, thus it should be in a directory at the end of 'runtimepath'.  For Unix
+that could be ~/.vim/after/compiler.
+
+==============================================================================
+
+Next chapter: |usr_42.txt|  Add new menus
+
+Copyright: see |manual-copyright|  vim:tw=78:ts=8:ft=help:norl: