Avoid strings with special characters in them. There are two reasons for this:
Umlauts are sometimes written ä, ö and ü and sometimes ae, oe and ue.
Even if the word is spelt the first way and you search for those characters or any other special characters such as French accents, you may not find it because these are special characters. They will probably appear in the source code as ä, ö and ü unless F. Page Express has got at them.
Be careful with words beginning with I or J. These were used interchangeably in the 1930s. So Igo Sym for example is often spelt Jgo Sym.
Note that all text is searched including HTML tags etc. So if you search for say Paris, it will also locate pages on which font=Paris is used.