Normalize Case of CSS selectors using C#

Question

I'm building a CSS Parser in C#, and I need to "normalize" the case of CSS selectors. What I mean by that is I want to make the tag names lowers case, but keep the classes and ids the way they are.

For example, if I had a string such as:

.Header Td.selected

I want to change normalize the case and change it to:

.Header td.selected

I want to preserve the case of the classes and id's, because in CSS they are case-sensitive. And I need to change the case-insensitive parts to lower case, to avoid storing duplicate CSS rules in my parser.

Therefore, I need some code to be able to distinguish the case-insensitive parts and change them to lower case. How do I do that?

Seems your questions already has the answer. You need to differentiate html tags from the rest, which shouldn't be difficult given there are only a certain number of tags. — Botond Botos
– Botond Botos, Commented Dec 30, 2016 at 16:52
HTML tag names are the only things in CSS not preceded by a period, a hash, bracket etc. So it shouldn't be too hard. — Mr Lister
– Mr Lister, Commented Dec 30, 2016 at 16:57
Keep in mind though that HTML is not case sensitive, but XML is. Treating a stylesheet meant for an XML file this way will mutilate it beyond recognition. — Mr Lister
– Mr Lister, Commented Dec 30, 2016 at 16:58
I need it for one application and it won't be applied to XML. — Osama
– Osama, Commented Dec 30, 2016 at 17:07

Markus Jarderot · Accepted Answer · 2017-01-01 10:55:06Z

1

selector = Regex.Replace(
    selector,
    @"(?<![#.:])(-?\b[^\W\d][-\w]*)",
    m => m.Value.ToLower())

It looks for identifiers that are not preceded by #, . or :.

-?\b[^\W\d][-\w]* or -?[^\W\d][-\w]* matches a CSS identifier, restricted to Basic Latin-1 (U+0000-U+007F).

h           [0-9a-f]
nonascii    [\240-\377]
unicode     \\{h}{1,6}(\r\n|[ \t\r\n\f])?
escape      {unicode}|\\[^\r\n\f0-9a-f]
nmstart     [_a-z]|{nonascii}|{escape}
nmchar      [_a-z0-9-]|{nonascii}|{escape}
ident       -?{nmstart}{nmchar}*

If the string is embedded in full css document, you could use

css = Regex.Replace(
    css,
    @"(?<![#.:])(-?\b[^\W\d][-\w]*)(?=(?:\s*(?:[+>,]|[#.:]?-?[^\W\d][-\w]*|\[.*?]))*\s*\{)",
    m => m.Value.ToLower())

It will make sure the word is part of the selector, and not the declarations. For it to match, the selector have to be followed by {.

edited Jan 1, 2017 at 10:55

answered Jan 1, 2017 at 10:28

Markus Jarderot

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