@Section
   @Title { "@Begin" and "@End" }
   @Tag { begin }
@Begin
@PP
The body of a symbol @Code "@Sym" may be enclosed in @@Begin and
begin. @Index { @@Begin symbol }
end. @Index { @@End symbol }
@@End @Code "@Sym" instead of the more usual braces:
@ID @Code {
"def @Section"
"    named @Title {}"
"    right @Body"
"@Begin"
"    @Title //2v @Body"
"@End @Section"
}
They may also enclose the right or body parameter of a symbol invocation:
@ID @Code {
"@Chapter"
"    @Title { Introduction }"
"@Begin"
"This subject needs no introduction."
"@End @Chapter"
}
Apart from their utility as documentation aids, these forms allow Basser
Lout to pinpoint mismatched braces, which can otherwise create total
havoc.  For this reason, they should enclose the major parts of documents,
such as chapters and sections.  Note that braces cannot be
replaced by @@Begin and @@End in general.
@End @Section