One search pass can produce a summary of the searchable features of documents, and subsequent searches will never need to read those documents again. This makes searching much cheaper. Other operating systems provide similar utilities. There are many different ways of specifying just what you are searching for. These tend to be more useful for finding highly structured data than for identifying conceptual contents.
Phrase searches are simply searches allowing multi-word terms.
Regular expression searches can certainly do this, but so can some simpler systems. How close is often a search option. Word stems are sometimes used instead of actual words. Conceptual searches find documents covering similar topics by recognizing words that are similar in meaning. This type of search requires integrating some sort of thesaurus into the search engine.