The WWP uses the extent= attribute of <gap> to indicate the extent of omitted material, measured in letters, lines of text, or pages. For information on indicating omitted letters or lines, see the general entry on <gap>.
The most complex use of the extent= attribute on <gap> is to indicate pages which are omitted before and after an excerpt. Within the extent= attribute, we record both the collation sequence and the pagination sequence of the omitted pages, separated by a semicolon, with the collation sequence first. The easiest way to show how to do this is with an example. For even more detailed information on special and difficult cases, see 197.
The basic formula is as follows: the list of omitted signatures, followed by a semicolon and a space, then the range of omitted pages introduced by “pp. ” There should be no spaces after commas within the signature and page series, to facilitate processing. A finished example would look like this:
<gap extent="&pgr;3,A-Z4,Aa-Zz4,Aaa-Ooo4,Ppp; pp. i-xiv,1-658"/>
See the example for a detailed explanation.