The various 'extract_...' subroutines may be used to extract a delimited
substring, possibly after skipping a specified prefix string. By
default, that prefix is optional whitespace ('/\s*/'), but you can
change it to whatever you wish (see below).The substring to be extracted
must appear at the current 'pos' location of the string's variable (or
at index zero, if no 'pos' position is defined). In other words, the
'extract_...' subroutines _don't_ extract the first occurrence of a
substring anywhere in a string (like an unanchored regex would). Rather,
they extract an occurrence of the substring appearing immediately at the
current matching position in the string (like a '\G'-anchored regex
would).