Updates the passed attributes without changing the other existing attributes
Class Details
[line 43]
HTML class for an advanced checkbox type field
Basically this fixes a problem that HTML has had where checkboxes can only pass a single value (the value of the checkbox when checked). A value for when the checkbox is not checked cannot be passed, and furthermore the checkbox variable doesn't even exist if the checkbox was submitted unchecked.
It works by prepending a hidden field with the same name and another "unchecked" value to the checbox. If the checkbox is checked, PHP overwrites the value of the hidden field with its value.