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\section{Vocabulary}
\label{glossary}
\label{vocabulary}

{\bf Template} is an informal term meaning a template definition, a
template instance or a template class.  A {\bf template definition} is what
the human {\bf template maintainer} writes: a string consisting of text,
placeholders and directives.  {\bf Placeholders} are variables that will be
looked up when the template is filled.  {\bf Directives} are commands to be
executed when the template is filled, or instructions to the Cheetah compiler.  
The conventional suffix for a file containing a template definition is 
{\bf .tmpl}.

There are two things you can do with a template: compile it or fill it.
{\bf Filling} is the reason you have a template in the first place:
to get a finished string out of it.  Compiling is a necessary prerequisite: the
{\bf Cheetah compiler} takes a template definition and produces Python code
to create the finished string.  Cheetah provides several ways to compile
and fill templates, either as one step or two.

Cheetah's compiler produces a subclass of \code{Cheetah.Template}
specific to that template definition; this is called the {\bf generated
class}.  A {\bf template instance} is an instance of a generated class.

If the user calls the \code{Template} constructor directly (rather than a
subclass constructor), s/he will get what appears to be an instance of 
\code{Template} but is actually a subclass created on-the-fly.

The user can make the subclass explicit by using the ``cheetah compile''
command to write the template class to a Python module.  Such a module is
called a {\bf .py template module}.

The {\bf Template Definition Language} -- or the ``Cheetah language'' for short
-- is the syntax rules governing placeholders and directives.  These are
discussed in sections \ref{language} and following in this Guide.

To fill a template, you call its {\bf main method}.  This is normally
\code{.respond()}, but it may be something else, and you can use the
\code{\#implements} directive to choose the method name.  (Section
\ref{inheritanceEtc.implements}.

A {\bf template-servlet} is a .py template module in a Webware servlet
directory.  Such templates can be filled directly through the web by requesting
the URL.  ``Template-servlet'' can also refer to the instance being filled by
a particular web request.  If a Webware servlet that is not a
template-servlet invokes a template, that template is not a template-servlet
either.

A {\bf placeholder tag} is the substring in the template
definition that is the placeholder, including the start and end delimeters (if
there is an end delimeter).  The {\bf placeholder name} is the same but without
the delimeters.  

Placeholders consist of one or more {\bf identifiers} separated by periods
(e.g., \code{a.b}).  Each identifier must follow the same rules as Python
identifiers; that is, a letter or underscore followed by one or more letters,
digits or underscores.  (This is the regular expression
\verb+[A-Za-z_][A-Za-z0-9_]*+.)

The first (or only) identifier of a placeholder name represents a {\bf
variable} to be looked up.  Cheetah looks up variables in various {\bf
namespaces}: the searchList, local variables, and certain other places.  The
searchList is a list of objects ({\bf containers}) with attributes
and/or keys: each container is a namespace.  Every template instance has
exactly one searchList.  Identifiers after the first are looked up only in
the parent object.  The final value after all lookups have been performed is
the {\bf placeholder value}.

Placeholders may occur in three positions: top-level, expression and LVALUE.
{\bf Top-level} placeholders are those in ordinary text (``top-level text'').
{\bf Expression} placeholders are those in Python expressions.  
{\bf LVALUE} placeholders are those naming a variable to receive a value.
(LVALUE is computerese for ``the left side of the equal sign''.)  Section 
\ref{language.placeholders.positions} explains the differences between these
three positions.

The routine that does the placeholder lookups is called the {\bf NameMapper}.
Cheetah's NameMapper supports universal dotted notation and autocalling.
{\bf Universal dotted notation} means that keys may be written as if they were
attributes: \code{a.b} instead of \code{a['b']}.  {\bf Autocalling} means that
if any identifier's value is found to be a function or method, Cheetah will
call it without arguments if there is no \verb+()+ following.  More about the
NameMapper is in section \ref{language.namemapper}.

Some directives are multi-line, meaning they have a matching {\bf \#end} tag.
The lines of text between the start and end tags is the {\bf body} of the
directive.  Arguments on the same line as the start tag, in contrast, are
considered part of the directive tag.  More details are in section
\ref{language.directives.syntax} (Directive Syntax Rules).

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