Fragment Search is a Greasemonkey script for Firefox which allows people to create URLs which link to content within a page without having control over that page.
Fragment identifiers in HTTP URIs have been historically used to link to a name or ID within a document’s markup. For example, http://www.mozilla.org/MPL/relicensing-faq.html#why-relicensing finds the HTML construct <a name="why-relicensing"> in the page in question.
This is historically true, although RFC 1738, the URL RFC, doesn’t actually seem to mandate it. Fragment identifiers are specced at a high level in RFC 3986, but that doesn’t say what they should be used for either. (If you know where this is specced, please let me know.)
But what do you do if the document doesn’t have a name or ID where you want to link, and you don’t have control of the document (as is the case for most people and most documents)? My suggestion is to extend the syntax of the fragment identifier using a character which is illegal in names/IDs (“!”), and which conforming browsers can use to trigger a textual search of the page contents. So, for example, http://www.gerv.net/#!s!design searches for the word “design” on the front page of gerv.net.
Clearly, this is just a proof of concept. It needs to be built into browsers to be generally useful. But please do try it out and let me know what you think.