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One of the features of HTML5 is the ability to validate most user data without relying on scripts.
This is done using validation attributes on form elements, which allow you to specify rules for a form input like whether a value needs to be filled in, the minimum and maximum length of the data, whether it needs to be a number, an email address, etc., and a pattern that it must match.
If so, it allows it to be submitted to the server and (usually) saved in a database; it not, it gives you error messages to explain what you've done wrong (provided you've done it right).
In addition to AMP validity, you may also want to confirm that your AMP document is discoverable to third-party platforms.If the entered data follows all those rules, it is considered valid; if not, it is considered invalid.* * Other expressions that are noted include: * * Double-mustache annotations in text content.The annotation must be the only * content in the tag, compound expressions are not (currently) supported.* * * * Only immediate host properties can automatically trigger side-effects.
Some editors, including Emacs (look for compile command and compilation mode), can interpret this format and let you jump to the errors in the original file.