There are also u"strings" which are unicode, and there
are ur"...." for unicode raw strings. These are described
in the current version of the Python Tutorial by
Guido van Rossum in section 3.1.3 (at the Python.org
website).

It is also worth nothing that these strings are Python
objects and that one can invoke string methods on them
just as one would through a variable. I can say:

x="This is a STRING".lower()

... just as easily as:

x="This is a STRING"
x=x.lower()

(And Unicode strings have .encode() methods to
return their ASCII, Latin-1, UTF-8 and UTF-16
representations).

You should perhaps also mention that the raw switch is especially useful for Window's path names and for regular expressions.

Why? Premise --- I don't know a thing about Python, but here it's just quoting/escaping. In no point of the section is said about a special function of backslash as an escape character. If you need a special token in front of a string to put raw backslashes in it, I argue, in ordinary strings backslash is used as a *meta*character, perhaps to do some escaping. But the text does not speak about it. More in general, I feel this subsection is not very clear. You say how to escape character/sequence x with character/sequence y, and y with z, but without coming to fixpoint. For instance, how do you escape triple quotes? How about if I want to put in the *same* string ", ', """, \?

Backslash will still escape " or ' in a r'raw string'. This feature was designed for regular expressions, not Windows path names.