Selectors should be case insensitive

[willmcgugan]

It looks like selectors insist on being lower-case, which means that if you use upper case in an ID it won't match. Possibly true of classes as well. Need to investigate.

Discussed in #1041

^{Originally posted by mindset-team October 28, 2022}
There's seems to be some case sensitivity issue with query/query_one. Here's an example app where widget id must be lower-cased in order to return a valid query result (vs. a NoMatches exception). The query selector seems to be case-insensitive.

from textual.app import App
from textual.widgets import Static

class GridLayoutExample(App):
    def compose(self):
        yield Static("some text here..", id="One")

    async def on_key(self, event):
        print(f'{self.query_one("#One")=}')

app = GridLayoutExample()

if __name__ == "__main__":
    app.run()

Above, on_key is simply used to trigger the query event and textual console opened in another terminal to monitor print output.
The code above fails with NoMatches: No nodes match <DOMQuery GridLayoutExample(title='GridLayoutExample') filter='#One'

However, changing id=One to id=one (in compose method yielding the static widget) works, no exception raised and console printout is valid:

[20:58:32] PRINT                                                                                                           latout.py:13
self.query_one("#One")=Static(id='one')

Is this behavior expected? It seems counter-intuitive that a selector would be case insensitive, but id would be coerced to be lower-cased for a query to work. I couldn't find any reference to case-[in]sensitivity in the textualize.io guide, or on github (after a quick review of the textual css parsing code and def query).

Not sure this elevates to a bug (and anyway maintaining all ID's in lower-case would avoid this issue) but since many of the examples have #One, #Two identifiers throughout the docs, the issue seems to merit a discussion here, a clear instruction in the docs, or designating as a bug to fix. Thoughts?

[davep]

After implementing this, and then having a chat about it in the office, we've decided that we'll follow the Web and do the opposite: case sensitivity will be fully-enforced for IDs (we should also check this for classes, etc, but for the moment this is about IDs).

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