invalid parsed selector, question about url() and built-in types

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Hello,

I'm using css lib to parse styles uploaded by users and then do some validation rules. First problem is about inproperly parsed selectors, for example:

```
#editTemporaryPriceList,
#addTemporaryPriceList,
#addPriceList { font-size: 1.2em; display: block; color: #333; text-decoration: underline; margin-top: 10px; padding-bottom: 3px; }
```

is parsed as:

```
(None, {'pseudo': [], 'attrib': [], 'hash': ['editTemporaryPriceList'], 'class': []})
(None, {'pseudo': [], 'attrib': [], 'hash': ['#addTemporaryPriceList'], 'class': []})
(None, {'pseudo': [], 'attrib': [], 'hash': ['#addPriceList'], 'class': []})
```

(# at the begging of 'hash' in two selectors)

The second problem is about attributes with url(). Why url() is stripped from value?

Third and the last problem is about built-in types. For example Percentage, Length, Rgb. I'm trying to create cleaned sheet from CSSStyleSheet, but i'm unable to check if attribute value is type of Length or other. When I import those classes from codetalker, 'isinstance' always return False and i need to do some hasattr checks to discover value's type. Is there any other way to do that?

It would be great if css could work in both ways (parse and print).

Inizia riproducendo i tre esempi con il CSS parser e CSSStyleSheet, quindi esamina il selector, il valore di url() e la gestione dei tipi incorporati di codetalker. Confronta l'output analizzato con il CSS originale e considera completato il lavoro quando i selector e i valori di url() vengono preservati e vengono esposti controlli di tipo affidabili; aggiungi una copertura di regressione per ogni caso.

Scritto dal modello di indicizzazione a partire dal testo della issue.