I've been having discussions with 'people' again and it's resulted in the following stupid question:
Can you only have 1 <h1> tag and then one of each of the others in descending order on the page?

i.e.
<h1>Title
<h2>Sub title
<h3>Other heading

Thanks in advance.
P

You don't have to restrict yourself to one <h1> tag. The <h1> tag says that this is the header the title for the page. There may be cases however that your page has two completely distinct content areas on the site. In this case it is acceptable to use another <h1> tag.

The next levels divide up the subsections of the page. If you have many subsections under a <h1> you can use many <h2>'s and for their conten, you can divide them by <h3>'s and <h4>'s etc.

<h1> Main content title
<h2>Subsection
<h3>sub sub section
<h3>sub sub section
<h4> Sub sub sub section
<h4> sub sub sub section
<h2> subsection
<h1>Completely new content -- rarely needed, you should proabably split the page
<h2>Subsection
<h3>sub sub section
<h3>sub sub section
<h4> Sub sub sub section
<h4> sub sub sub section
<h2> subsection


You treat them sort of like you treat html tags. <h1> has child <h2>'s and <h2> has hcild <h3>'s etc.

In terms of syntactical correctness (HTML validation), it makes no difference. You can use <h1> -- <h6> in any order, any number of times, or omit them altogether.

In terms of semantics (meaningful markup), you should never skip a heading level; use headings in the way indicated by Rakuli's example. The first heading on the page (if you use headings at all) should always be an <h1>. The next heading should not be an <h3> (you need an <h2> first).

Sometimes styling concerns may tempt you to skip a heading. Resist this temptation, and restyle the headings instead where necessary. For example: I change the formatting of <h2>s in my footer and sidebar, so that they look like <h3>s. This maintains a logical document structure, while also allowing sensible styles (the normal <h2> style would look wacko if applied in the sidebar or footer).

I recommend using only one <h1>. By using a single, top-level heading, you indicate what the entire page is about. The page is the atomic unit of the web; divide your content logically into pages.

On the other hand, you might reasonably argue that site-wide areas (such as preferences/nav) should not be categorised under the page title. That might lead one towards using multiple <h1>s:

<h1>Content title</h1>
<h2>Sub-topic</h2>

<h1>Preferences/nav</h1>

Thanks guys!