When interpreting supplied pattern as perl regular expression grep displays
match across multiple lines --- in spite of the ^beginning-of-line character
specified in the pattern.

Actual result:
$ echo -e "\n\n\n   foo" | grep -P '^\s*foo'



   foo

Expected result:
The leading empty lines should be omitted from the output:

$ echo -e "\n\n\n   foo" | grep -P '^\s*foo'
   foo