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Add a note about case sensitivity in regexps

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Kovid Goyal 2022-05-13 17:05:52 +05:30
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manual/regexp.rst
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@ -60,7 +60,11 @@ You can of course do that: Just put a backslash in front of any special characte
So, what are the most useful sets? So, what are the most useful sets?
------------------------------------ ------------------------------------
Knew you'd ask. Some useful sets are ``[0-9]`` matching a single number, ``[a-z]`` matching a single lowercase letter, ``[A-Z]`` matching a single uppercase letter, ``[a-zA-Z]`` matching a single letter and ``[a-zA-Z0-9]`` matching a single letter or number. You can also use an escape sequence as shorthand: Knew you'd ask. Some useful sets are ``[0-9]`` matching a single number,
``[a-z]`` matching a single lowercase letter, ``[A-Z]`` matching a single
uppercase letter, ``[a-zA-Z]`` matching a single letter and ``[a-zA-Z0-9]``
matching a single letter or number. You can also use an escape sequence as
shorthand:
``\d`` ``\d``
is equivalent to ``[0-9]`` is equivalent to ``[0-9]``
@ -75,8 +79,16 @@ Knew you'd ask. Some useful sets are ``[0-9]`` matching a single number, ``[a-z]
.. note:: .. note::
"Whitespace" is a term for anything that won't be printed. These characters include space, tabulator, line feed, form feed, carriage return, non-breaking spaces, etc. "Whitespace" is a term for anything that won't be printed. These characters include space, tabulator, line feed, form feed, carriage return, non-breaking spaces, etc.
.. note::
The upper and lower case sets may match both upper and lowercase if the
setting to make searches case insensitive is enabled. Such settings are
found, for instance in Preferences->Searching in calibre itself and on the
Search panel in the calibre viewer and editor programs.
As a last note on sets, you can also define a set as any character *but* those in the set. You do that by including the character ``"^"`` as the *very first character in the set*. Thus, ``[^a]`` would match any character excluding "a". That's called complementing the set. Those escape sequence shorthands we saw earlier can also be complemented: ``"\D"`` means any non-number character, thus being equivalent to ``[^0-9]``. The other shorthands can be complemented by, you guessed it, using the respective uppercase letter instead of the lowercase one. So, going back to the example ``<p[^>]*>`` from the previous section, now you can see that the character set it's using tries to match any character except for a closing angle bracket. As a last note on sets, you can also define a set as any character *but* those in the set. You do that by including the character ``"^"`` as the *very first character in the set*. Thus, ``[^a]`` would match any character excluding "a". That's called complementing the set. Those escape sequence shorthands we saw earlier can also be complemented: ``"\D"`` means any non-number character, thus being equivalent to ``[^0-9]``. The other shorthands can be complemented by, you guessed it, using the respective uppercase letter instead of the lowercase one. So, going back to the example ``<p[^>]*>`` from the previous section, now you can see that the character set it's using tries to match any character except for a closing angle bracket.
But if I had a few varying strings I wanted to match, things get complicated? But if I had a few varying strings I wanted to match, things get complicated?
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