Using colons (:) in a form-tag name is allowed, but not recommended.
While the primary role of a form-tag name is to specify the name attribute value of a form control element, it is also used as a variable part of a CSS ID selector or class selector to connect with the form control. If a colon is used in a selector, the browser may confuse the colon with the prefix of a pseudo-class, leading to unexpected behavior.
In usual use cases, you shouldn’t need to use colons in a form-tag name. If you get this warning message, it might be because you have misconfigurations in form-tags. Check to see if your form-tags are in the correct format.
The following form-tag is an example that includes a common mistake:
[text* class:required your-name "John Smith"]
Perhaps your intention is to set the form-tag name to your-name, but this form-tag does not work like that. In this form-tag, class:required is the name. As explained in Form-tag syntax, the name of a form-tag is the second word in the tag, and must come before other options and values.
The correct format would be:
[text* your-name class:required "John Smith"]
Also, if you’ve corrected your form-tags, don’t forget that you’ll need to replace the corresponding mail-tags in the Mail tab panel.