REFind(reg_expression, string, start)
Returns the position of the first occurrence of a regular expression in a string starting from the specified position. Returns 0 if no occurrences are found. This search is case-sensitive.
Regular expression used for search. This regular expression can include POSIX-specified character classes (for example, [:alpha:], [:digit:], [:upper:], and [:lower:]).
String being searched.
Starting position for the search.