These checks perform basic validation routines like checking if a field is filled out or if a field value is a valid email address.
These error checks allow various checks suitable for strings, f.e. checking if a string is at least 10 characters long or if a string contains a specific word.
If you want to perform error checks on numbers, e.g. if a field value is a valid integer, these checks are right for you.
Array checks are useful when dealing with arrays of check boxes and similar cases.
Using these error checks you can force the user to enter a valid date or time. You can even check for a valid date range.
These checks validate a captcha string generated by an extension of you choice. Please have a look at How to set up spam protection for more details.
These are all available error checks dealing with file uploads. You can restrict allowed file types, set min and max uploadable files for one upload field and more.
These checks allow you to ensure that a database record exists or doesn't exist. This is useful for unique constraints like username or email address.