Validation class: alpha-dash-comma - ?

[eluser]tinawina[/eluser]
Hi -

I have a tag class that runs our site's tagging utility. I want to allow people to add tags that include alphanumeric characters, dashes and underscores which the validation class already let's me do easily via "alpha-dash". We are separating tags (which can be phrases, etc.) with a comma. So I want submissions to include not only alphanumeric characters, dashes, and underscores but also commas.

I went into the validation library to see if there was an easy way to do this. Here's the validation library method for alpha-dash:

Code:

function alpha_dash($str)
{
    return ( ! preg_match("/^([-a-z0-9_-])+$/i", $str)) ? FALSE : TRUE;
}

Of course, I was hoping this would be as easy as just adding a related error message in the validation_lang file, and then adding a new method to the validation library like so:

Code:

function alpha_dash_comma($str)
{
    return ( ! preg_match("/^([-a-z0-9_-,])+$/i", $str)) ? FALSE : TRUE;
}

But I get this error message:

"Message: preg_match() [function.preg-match]: Compilation failed: range out of order in character class at offset 13"

Anybody have any clues re: why I'm getting this error and what I need to do to make this change? Any help - much appreciated!