Invalid characters end up in CSS ID tag, form_id_clean() does not handle enough cases

Oops, I prematurely hit Save.

The end result CSS ID would be:
Heres-is-a-valid-radio-button-item;-however,-the-CSS-ID-tag-will-put-a-semicolon-and-command-in-the-id

This is invalid as far as I can tell and cannot be properly modified via CSS.

I also discovered that other symbols such as the period ., parenthesis (), and so on.. will also end up in the ID tag when it should not.

After doing some searching around in the code, I could not find a place in CCK where this is being set.

Instead, I looked into Drupal core and found the function form_id_clean: http://api.drupal.org/api/function/form_clean_id/6

The relevant line is:

<?php
$id = str_replace(array('][', '_', ' '), '-', $id);
?>

That is far too few cases.

Instead, something like the following could be used:

<?php
$id = str_replace(array('][', '_', ' ', '`', '~', '!', '@', '#', '$', '%', '^', '&', '*', '(', ')', '+', '=', '[', '{', '}', ']', '|', '\\', ';', ':', '\'', '"', '<', ',', '>', '.', '?', '/'), '-', $id);
?>

But the next problem here is different languages.
So, I decided that a regular expression would work better as this allows for more language independent symbol replacements:

<?php
$id = str_replace(array('][', '_', ' '), '-', $id);
$id = preg_replace('/\W/i', '-', $id);
?>

I left the existing str_replace for two reasons:
1) the underscore symbol '_' is considered a Word character and will not get replaced by the given preg_replace function
2) I don't know what is going on with the '][' case.

I have a patch for review that fixes this case.

Unfortunately the patch you provided breaks things like views module's Live preview.

My patch works without any problems that I have noticed.

As far as your patch, I did a diff between a working views view and your backport shows that:
Before your patch the relevant view html looks like: edit-live-preview
After your patch the relevant view html looks like: edit-live_preview

This latest one is working so far.