I am creating a registration form which requires a password with at least 1 special character. The Chrome password manager does not suggest a password with a special character and fails validation. I would like for password managers to be able to know what the requirements are for passwords. I have read this SO question and tried using the 'pattern' attribute, but I experienced the same issues described in the comment, only 'maxlength' seems to have any effect, anything specified by 'pattern' was ignored.
How can I tell password managers how to suggest a valid password?
It is one of the reasons, why complex password rules are not recommended anymore, important is only a minimum password length and a check against the most often used passwords (the minimum length will already rule out most of the well known passwords though).
Besides infering with password managers/schemes, users will often fall back to less safe passwords instead of stronger ones if the rules are too cumbersome, like "Password#". Long password phrases can be remembered easily by users, but complex passwords will be forgotten in an instant (unless they are stored in a password manager, which would not need such rules to produce safe passwords...).