Returns the filename extension.
+=head3 head (list)
+
+For example:
+
+ head (["a", "b", "c"]) ⇒ "a"
+
+Returns the head (first) element of the list.
+
=head3 join (list1, list2)
For example:
this function since goals automatically flattens lists within lists
into simple lists in many cases.
+=head3 realpath (filename)
+
+For example:
+
+ realpath ("./tests") ⇒ "/home/user/tests"
+
+Run the L<realpath(1)> command to return the resolved absolute path of
+the C<filename> parameter.
+
=head3 sort (list)
For example:
that C<from> is a regular expression, specifically a L<sed(1)>
extended regular expression.
+=head3 tail (list)
+
+For example:
+
+ tail (["a", "b", "c"]) ⇒ ["b", "c"]
+
+Returns the tail (all except first) elements of the list.
+
=head3 wildcard (pattern)
For example: