What does a leading `\x` mean in a Python string `\xaa`

Question

What is difference between 'aa' and '\xaa'? What does the \x part mean? And which chapter of the Python documentation covers this topic?

Answer 1

The leading \x escape sequence means the next two characters are interpreted as hex digits for the character code, so \xaa equals chr(0xaa), i.e., chr(16 * 10 + 10) -- a small raised lowercase 'a' character.

Escape sequences are documented in a short table here in the Python docs.

Answer 2

That's unicode character escaping. See "Unicode Constructors" on PEP 100