string() has no FIND operation for regular expressions
For some reason, there is a FIND operation but it does not accept regular expressions. The only regular expression operations do matches, but do not return the index of the regex occurrence. To get the index, you have to give up regular expressions. Technically, one could do a REGEX MATCH followed by a FIND using the result to find the exact expression as it occurs in the original string, but this seems programmer-hostile.