PmWiki's markup translation engine is handled by a set of rules; each rule searches for a specific pattern in the markup text and replaces it with some replacement text. Internally, this is accomplished by using PHP's "preg_replace" function.

Rules are added to the translation engine via PmWiki's Markup() function, which looks like

   Markup($name,$when,$pattern,$replace)

where $name is a unique name (a string) given to the rule, $when says when the rule should be applied relative to other rules, $pattern is the pattern to be searched for in the markup text, and $replace is what the pattern should be replaced with.

For example, here's the code that creates the rule for ''emphasized text'' (in scripts/stdmarkup.php):

   Markup("em","inline","/''(.*?)''/","<em>$1</em>");

Basically this statement says to create a rule called "em" to be performed with the other "inline" markups, and the rule replaces any text inside two pairs of single quotes with the same text ($1) surrounded by <em> and </em>.

The first two parameters to Markup() are used to specify the sequence in which rules should be applied. The first parameter provides a name for a rule -- "em" in the example above. We could've chosen other names such as "''", or even "twosinglequotes". In general PmWiki uses the markup itself to name the rule (i.e., PmWiki uses "''" instead of "em"), but to keep this example easier to read later on we'll use a mnemonic name for now.

The second parameter says that this rule is to be done along with the other "inline" markups. PmWiki divides the translation process into a number of phases:

   _begin          start of translation
   fulltext        translations to be performed on the full text            
   split           conversion of the full markup text into lines to be processed
   directives      directive processing
   inline          inline markups
   links           conversion of links, url-links, and WikiWords     
   block           block markups
   style           style handling       
   _end            end of translation

Thus, specifying "inline" for the second parameter says that this rule should be applied when the other "inline" rules are being performed. If we want a rule to be performed with the directives -- i.e., before inline rules are processed, we would specify "directives" for the second parameter.

Here's a rule for @@monospaced@@ text

   Markup("@@","inline","/@@(.*?)@@/","<code>$1</code>");

and for a [:comment ...:] directive that is simply removed from the output:

   Markup("comment","directives","/\\(:comment .*?:\\)/",'');

Okay, now how about the rule for '''strong emphasis'''? We have to be a bit careful here, because although this translation should be performed along with other inline markup, we also have to make sure that the rule for ''' is handled before the rule for '', because ''' also contains ''. The second parameter to Markup() can be used to specify the new rule's relationship to any other rule:

   Markup("strong","<em","/'''(.*?)'''/","<strong>$1</strong>");           

This creates a rule called "strong", and the second parameter "<em" says to be sure that this rule is processed before the "em" rule we defined above. If we wanted to do something after the "em" rule, we would use ">em" instead. Thus, it's possible to add rules at any point in PmWiki's markup translation process in an extensible manner. (In fact, the "inline", "block", "directives", etc., phases above are just placeholder rules used to provide an overall sequence for other rules. Thus one can use "<inline" to specify rules that should be handled before any other inline rules.)

If you want to disable available markup just call e.g.:

   Markup("strong","<em");           

The lack of a pattern & replacement parameters indicates that you simply wish to disable the markup.

PmWiki's default markup rules are defined in the scripts/stdmarkup.php file. To see the entire translation table as the program is running, the scripts/diag.php module adds "?action=ruleset", which displays the set of defined markup rules in the sequence in which they will be processed. You can see it at CustomMarkup?action=ruleset.

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