Substitution string element. Optional in
Defines a replacement string for the matched string or substring in the path or query.
If the pattern expression includes subexpressions (delimited with parentheses), the first matched substring is replaced with the substitution string. If the pattern expression does not include subexpressions, the entire matched string is substituted.
<expression> is empty or absent, the substitution string is appended to the path or query.
<substitution> is empty, the matched string or substring is removed. If
<substitution> is not specified, the path or query string is not modified.
The substitution string must not contain literal < and & characters. These reserved characters can be encoded with
<, respectively, or the entire string can be enclosed in an XML
<substitution><![CDATA[&text=<Hello, world!>]]></ substitution>