2.1.13 [HTML5:2014] Section 3.2.5.9 Embedding custom non-visible data with the data-* attributes

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V0022: A data- attribute that contains an uppercase letter after a dash does not insert a dash before the character

The specification states:

 3.2.5.9 Embedding custom non-visible data with the data-* attributes
     ...
     The algorithm for setting names to certain values
         ...
         4. For each uppercase ASCII letter in name, insert a U+002D HYPHEN-MINUS 
            character (-) before the character and replace the character with the same 
            character converted to ASCII lowercase.

All document modes (All versions)

A data- attribute that contains an uppercase letter after a dash does not insert a dash before the character.

V0023: A SyntaxError is not thrown when setting a data- attribute that contains a dash in the name

The specification states:

 3.2.5.9 Embedding custom non-visible data with the data-* attributes
     ...
     The algorithm for setting names to certain values
         ...
         3. If name contains a "-" (U+002D) character followed by a lowercase ASCII 
            letter, throw a SyntaxError exception and abort these steps.

All document modes (All versions)

A SyntaxError is not thrown when setting a data- attribute that contains a dash in the name (e.g. data-to-string).