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What are valid values for the id attribute in HTML?

ID and NAME tokens must begin with a letter ([A-Za-z]) and may be followed by any number of letters, digits ([0-9]), hyphens ("-"), underscores ("_"), colons (":"), and periods (".").

Id must match [A-Za-z][-A-Za-z0-9_:.]*

Must Start with A-Z or a-z characters
May contains _(hyphen), :(colan) and .(dot)