The EOL_SPAN_REGEXP rule is similar to the EOL_SPAN rule except the match sequence is taken to be a regular expression. In addition to the attributes supported by the EOL_SPAN tag, the HASH_CHAR attribute must be specified. It must be set to the first character that the regular expression matches. Note that this disallows regular expressions which can match more than one character at the start position.

Regular expression syntax is described in Appendix E.