Returns the offset of where the last m//g search left off for the variable
in question ($_
is used when the variable is not specified). Note that
0 is a valid match offset. undef indicates that the search position
is reset (usually due to match failure, but can also be because no match has
yet been run on the scalar). pos directly accesses the location used
by the regexp engine to store the offset, so assigning to pos will change
that offset, and so will also influence the \G
zero-width assertion in
regular expressions. Because a failed m//gc match doesn't reset the offset,
the return from pos won't change either in this case. See perlre and
perlop.