Forms

'Single quotes are fine.'
"Double quotes is the equivalent, but it can use ' in it."
"""Tripple quote can be used to multiple lines string.
	And it also usually can be used as annotation."""

Feature

String is a Container, too.

len
Element selection expression. And an element of it is still string, like ‘a’, ‘0’ and so on.
in and not in. They can be used to match substring.