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$_SYNTAX_... VARIABLES
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  DESCRIPTION
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    The $_SYNTAX_... variables, such as $_SYNTAX_OPEN_DO and
    $_SYNTAX_CLOSE_DISPLAY are used to define the tag syntax of the PTM
    language. Although they are publicly accessible, there is little reason to
    ever use them. They contain the regular expression text used to parse the
    different PTM tag types out of your PTM/HTML documents and replace them with
    the appropriate HTML equivalent of your requested PTM/Perl requests.

    For crafty Perl users only -- modifying these regular expressions in the PPA
    (PTM Parser Application) [ptm.cgi] allows you to modify the PTM language to
    fit your own programming preferences. It is not recommended for normal
    users, but is possible to suit the language to match your own needs as a
    developer. But a side-note: these sorts of modifications are supported in no
    way and should only be attempted by Perl hackers that feel like having a
    little fun with their own PTM version.