2.7.1 library(help): Text based manual
All Application Manual Name SummaryHelp

Availability::- use_module(library(help)).(can be autoloaded)
Source[det]apropos(+Query)
Print objects from the manual whose name or summary match with Query. Query takes one of the following forms:
Type:Text
Find objects matching Text and filter the results by Type. Type matching is a case intensitive prefix match. Defined types are section, cfunction, function, iso_predicate, swi_builtin_predicate, library_predicate, dcg and aliases chapter, arithmetic, c_function, predicate, nonterminal and non_terminal. For example: 
?- apropos(c:close).
?- apropos(f:min).
Text
Text is broken into tokens. A topic matches if all tokens appear in the name or summary of the topic. Matching is case insensitive. Results are ordered depending on the quality of the match.