6. The method of claim 1 , wherein the search expression is a first search expression; the other content items are first other content items; the user also uses a second content item, and the method further comprises: receiving, by the search expression generator, a constituent of the second content item, wherein the second content item is also a selected one of a web page, a post to a social networking site, a post to a blog, a post to an online bulletin board, a document, an electronic message, a product description, an entertainment description, or an advertisement, having text divisible into a plurality of subtexts; and generating a second search expression, by the search expression generator, based on the constituent of the second content item, to search second other content items, through execution of the second search expression, wherein the second search expression includes a hierarchy of a plurality of nested juxtaposition sub-expressions corresponds with nesting of subtexts of the constituent of the second content item; wherein the second search expression is to be applied by the search engine operated on the same or a different computer system, to the second other content items to generate a second search result.
7. The method of claim 6 , wherein the search result includes a constituent of a third content item or a fourth content item, to be recommended to the user.