The SEQ_REGEXP rule is similar to the SEQ rule except the match sequence is taken to be a regular expression. In addition to the attributes supported by the SEQ tag, the following attributes are supported:

HASH_CHAR and HASH_CHARS attributes are both optional, but you may only specify one, not both. If both are specified, HASH_CHARS is ignored and an error is shown. Whenever possible, use a literal prefix to specify a SEQ_REGEXP. If the starting prefix is always the same, use HASH_CHAR and provide as much prefix as possible. Only in rare cases would you omit both attributes, such as the case where there is no other reliable way to get the highlighting you need, for example, with comments in the Cobol programming language.

The regular expression match cannot span more than one line.

Regular expression syntax is described in Appendix E, Regular Expressions.

NOTE: c-style character escaping for literals (such as the tab char: \t) do not work as attribute values in XML. Use the XML character entity instead. For example: 	 instead of \t.

Here is a SEQ_REGEXP rule from moin.xml that uses the HASH_CHARS attribute, to describe a keyword (wikiword) that can start with any uppercase letter and contain lower case letters and at least one uppercase letter in the middle.

 		<SEQ_REGEXP HASH_CHARS="ABCDEFGHIJKLMNOPQRSTUVWXYZ" AT_WORD_START="TRUE"
 		TYPE="KEYWORD2">[A-Z][a-z]+[A-Z][a-zA-Z]+</SEQ_REGEXP>