Description:

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).