[theandrewbailey]

Is there even a use case where CSS needs to read any field's value? (Checkboxes and radio buttons have :checked.)

[kodablah]

It's about the selector, so the question should be rephrased to "Is there even a use case where CSS needs to select a node based on any field's value?". I think the answer is yes, but it can be limited. But it can become annoying to have a blacklist of attributes that aren't allowed to be selected on.

[sgc]

It's pretty common to check values of a field and set a color to the border etc. based on that, which I think is even very good ui. Maybe browsers should force restricted selectors only on some fields, which only allow limited matching based on predefined character classes or el1 === el2, since it sounds like this could be used for a cross site css attack (perhaps there already were some and I am ignorant).

[jakobegger]

Something like conditional formatting maybe? Eg. make negative values red?

Make an input field red when it contains an invalid character?

[theandrewbailey]

Sounds like the pattern attribute and :invalid selector on <input> will do that.

https://developer.mozilla.org/en-US/docs/Web/HTML/Element/in...

[thefifthsetpin]

What if it's valid? There's a reason we have the phrases "in the red" and "in the black."

Another example where reading the input might be nice:

  input[type="cc-number"][value^="4"]+.cc-system-icon {
    background-image: url('visa.png');
  }input[type="cc-number"][value^="5"]+.cc-system-icon {
    background-image: url('master-card.png');
  }

[dillondoyle]

I was also thinking along those lines, a way to LINT/validate form fields when JS is disabled, but seems like a very obscure and inefficient (use html5 validation + js, validate server side on submit)

[magnat]

It might be useful to show/hide certain parts of the form depending on a value selected in dropdown (SELECT) control. As for text input controls - perhaps to highlight the content when value matches expected (but not required) pattern.

[xab9]

it's an attribute matcher, the fact that value is an attribute (or prop or whatever, I don't care) is just sugar