Not really a question but I could not find a lot of information in the documentation or the existing contributed projects.
I have a form with SIREN / SIRET fields (those are identification numbers for french companies). A siren is 9 digits and a siret is 14. I could easily use standard widgets for the length but that was all.
So I created a custom widget starting with pbInput standard widget (workspace/default/web_widgets). I removed minLength, maxLength, type, min value, max value and and added an inputType property which value can be siren or siret (default: siren).