Questions on htags

A few questions on htags.

Length: I know its supposed to be a heading. But is there any opinion about the length you should use? 2-3 words only or can you use more for a more thorough description. Does the answer change the lower you go (i.e., h1 use only a few words, but h4, use a linger number of descriptive words)?

Use of lower hierarchy tags: I see discussion of h1-h3 tags...but what about the rest? Is there less or relatively little value to organizing things with h4, h5, h6 tags?

Thank you for your thoughts!

I think a rule of thumb is that if you can imagine it being a appropriate length for a book title, then it would be acceptable.

Probably 4 to 8 significant terms is about deal. Example:

vBSEO Helped My Traffic Grow by 400% in the First Four Months

Keywords in bold would be considered "significant terms".

heading tags should be used to structure your document.

the w3 validator has an outline option.