[whatwg] Web Forms: pattern attribute

[Michel Fortin]

Le 3 avr. 2006 à 19:33, Dean Edwards a écrit :

> Michel Fortin wrote:
>
>> Does that mean that a pattern attribute like "foo|bar" should  
>> translate to /^foo|bar$/ ? Wouldn't it make more sense it it was /^ 
>> (foo|bar)$/ with the parentesis?
>
> You have a point. Would implied parentheses cause any side effects?  
> None that I can think of...

Now that you mention it, it could. With a pattern like this:

     "(.).*\1"

which simply indicates that the first and the last characters must be  
the same, reference numbers won't refer to the right part. When the  
pattern get transformed to this:

     /^((.).*\1)$/

it makes `\1` a reference to the whole input text (the first  
parenthesis) rather than the first character (which has become the  
second parenthesis). This is not good.

So we will need to use a non-matching group `(?: ... )` instead:

     /^(?:(.).*\1)$/

Problem solved.


Michel Fortin
michel.fortin at michelf.com
http://www.michelf.com/