<<.preamble """What follows is a formal presentation of the syntax of the `\define` pragma, using [[railroad diagrams|Railroad Diagrams]]. A [[simpler overview|Macro Definitions in WikiText]] is also available.""">>
<$railroad text="""
"\define" space name params [:space] rest
"""/>
<<.place space>> denotes a sequence of [[whitespace characters|Filter Whitespace]].
The [[macro|Macros]]'s <<.place name>> is a sequence of non-whitespace characters other than `(` or `>`.
The parameter declaration list (<<.place params>>) has the following syntax:
<$railroad text="""
"(" [:sep] [:{ param sep }] ")"
"""/>
The parameter separator (<<.place sep>>) is any sequence of characters that does not match a <<.place param-name>>. Among other things, this includes commas, spaces and linefeeds.
A <<.place param-name>> is a sequence of letters (`A`--`Z`, `a`--`z`), digits (`0`--`9`), hyphens (`-`) and underscores (`_`).
Each individual <<.place param>> has the following syntax:
<$railroad text="""
param-name [: [:space] ":" [:space] default ]
")"
"""/>
The optional <<.place default>> value of a parameter is specified as follows:
The <<.place rest>> of the definition has the following syntax:
<$railroad text="""
( snippet | lf snippet lf "\end" [:space] ) lf
"""/>
<<.place lf>> denotes a linefeed.
The <<.place snippet>> is any sequence of characters that doesn't terminate the macro definition. That is to say, a single-line snippet cannot contain a linefeed, and a multi-line snippet cannot contain `\end` on a line of its own.
The snippet can contain placeholders with the following syntax:
