The SPAN_REGEXP rule is similar to the
        SPAN rule except the start sequence and optionally
        the end sequence are taken to be regular expressions. In addition to the
        attributes supported by the SPAN tag, the following
        attributes are supported:
HASH_CHAR - a literal string which must
                be at the start of a regular expression.
HASH_CHARS - a list of possible literal
                characters, one of which must match at the start of the regular
                expression.
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
        SPAN_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.
In addition, the END subtag supports the
        attribute REGEXP, which if set to
        TRUE, tells the highlighter to interpret the
        END text as a regular expression as well.
The regular expression match cannot span more than one line. Any
        text matched by groups in the BEGIN regular
        expression is substituted in the END string. See
        below for an example of where this is useful.
Regular expression syntax is described in Appendix E, Regular Expressions.
Here is a SPAN_REGEXP rule that highlights
        “read-ins” in shell scripts:
<SPAN_REGEXP HASH_CHAR="<" TYPE="LITERAL1" DELEGATE="LITERAL">
    <BEGIN><![CDATA[<<[\p{Space}'"]*([\p{Alnum}_]+)[\p{Space}'"]*]]></BEGIN>
    <END>$1</END>
</SPAN_REGEXP>Here is a SPAN_REGEXP rule that highlights
        constructs placed between <#ftl and
        >, as long as the <#ftl is
        followed by a word break:
<SPAN_REGEXP TYPE="KEYWORD1" HASH_CHAR="<" DELEGATE="EXPRESSION">
    <BEGIN><#ftl\b</BEGIN>
    <END>></END>
</SPAN_REGEXP>