Didn't read the previous thread, so please forgive me if I'm hitting
things already covered.

 1) The page begin should typically be recorded outside the <div>
    that indicates the preface, not inside.

 2) The page number (as written on the page) should be recorded in
    <fw>, not <ab>.

 3) The @corresp attribute is a pointer, not matcher. So in this case
    it should start with a sharp: "#KMG2Pref1".

Thus something like

| <pb xml:id="KMG2Pref1" n="01"/>
| <fw type="pageNumber" style="text-align:center;">- 1 -</fw>
| <div type="preface">
|   <lb/><head type="main" style="text-transform: uppercase;">Preface</head>
|   <p>[...]</p>
|   <!-- ... -->
| </div>
might do you well. Here the pb/@n gives you the page number as
counted, and the content of <fw> gives you the page number as it
appeared on the page. The use of fw/@style allows you to say that the
content was centered in the original, but there is absolutely nothing
wrong with your use of <space> to indicate how much horizontal space
precedes the page-number-as-written; I was just taking this
opportunity to show an alternative approach.

Same with my use of head/@style to show that "Preface" was in all
uppercase characters in the original: absolutely nothing wrong with
just recording it as "PREFACE". The mild advantage of the encoding
above is that I get to print it in title case ("print me the content
of <head>") or in all uppercase ("print me the content of head, but
apply the @style, too"). 

> may I ask for your opinion on a small matter:
> We are transcribing typescripts that have been edited by hand. Our TEI 
> documents are transformed to provide output for diplomatic 
> representations of the source texts.
> The question I have is about headings in <head> and page numbers. Right 
> now our TEI looks like this:
> <div type="preface">
>    <pb xml:id="KMG2Pref1" n="01"/>
>    <ab type="pagenumber"><space dim="horizontal" extent="62" unit="chars"/>- <anchor type="pagenumber" corresp="KMG2Pref1"/>-</ab>
>    <lb /><ab type="mainHeading">PREFACE</ab>
>    <p>
>      [...]
>    </p>
>      [...]
> </div>
> As you can see, in addition to <pb/> page numbers are also encoded in 
> <ab>. The reason is that sometimes we encounter page numbers that have 
> been edited by the author. Sometimes up to four times. This we want to 
> record, and it does not seem possible to do this solely in the 
> attributes of <pb/>. Headings right now are therefore also encoded with 
> <ab>.
> I would like to put headings in proper <head> elements. However <head> 
> cannot stand behind <ab>. At the moment I only see two solutions:
> 1) Can I put the information for page numbers into a <head> element, 
> too? In that case I would treat <head> more generally as an element for 
> some text at the top of a <div> and outside of the main body of text. 
> Then I would be able to add headings in additional <head> elements.
> 2) I stick to my solution with <ab> elements and don't use <head>.
> Thanks in advance for your opinions on this: that would really help me 
> in deciding on how to proceed.