Basically, that's a wildcard Find expression. The:
• [PR] says to find either P or R;
• [eu] says to find either e or u;
• [bv] says to find either b or v;
• [ils]{3} says to find any 3-letter combination consisting of i, l, and/or, s;
• [ehno]{2} says to find any 2-letter combination consisting of e, h, n, and/or o
• [ Ndo]{,1 3} says to find any 1- to 3-letter combination consisting of a space, N, d, and/or, o.
Whilst the character combination possibilities are almost endless, the reality is that, given the words used in the English language, such an expression is unlikely to Find anything other than 'Revision No' or 'Published' (with or without the trailing space for the latter).

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]