tidy-html5/README/ATTRIBUTES.md

Tidy Element Attributes

This is about adding a new attribute=value for one or more html element, here called tags.

Tidy supports a large number of attributes, first defined in tidyenum.h, to give it a value, then defined in attrs.c to give it a unique string name, and a function to verify the atrribute value. Then in attrdict.c the attribute is defined, giving what version(s) of html support this attribute. Finally, what tags support this attrinute, is done in tags.c, where each attribute is allowed on that tag, or not, in the tag_defs[] table.

So, to add a new attribute=value, on one or more existing tags, consists of the following simple steps -

1. tidyenum.h - Give the attribute an internal name, like TidyAttr_XXXX, and thus a value. While there were some initial steps to keep this TidyAttrId enumeration alphabetic, now just add the new TidyAttr_XXXX just before the last entry 'N_TIDY_ATTRIBS'.

2. attrs.c - Assign the string value of the attribute. Of course this must be unique. And then assign a function to verify the attribute value. There are already a considerable number of defined functions to verify specific attribute values, but maybe this new attribute requires a new function, so that should be written, and defined.

3. attrdict.c - If this attribute only relates to specific tags, then it should be added to their list. There are some general attributes that are allowed on every, or most tags, so this new attribute and value should be added accordingly.

4. tags.c - Now the new attribute will be verified for each tag it is associate with in the tag_defs[] table. Like for example the <button ...>, { TidyTag_BUTTON, ... has &TY_(W3CAttrsFor_BUTTON)[0] assigned.

So, normally, just changing 3 files, tidyenum.h, attrs.c, and attrdict.c, will already adjust tags.c to accept a new attribute=value for any tag, or all tags. Simple...

Now, one could argue that this is not the best way to verify every attribute and value, for every tag, but that is a mute point - that is how tidy does it!

; eof 20170205