To write unique code to handle input to or situations arising in a program that are somehow distinguished from normal processing. This would be used for processing of mode switches or interrupt characters in an interactive interface (as opposed, say, to text entry or normal commands), or for processing of hidden flags in the input of a batch program or filter. [Jargon File]

In addition suitable contents:
[ = ] [ ag ] [ al ] [ am ] [ an ] [ ar ] [ arc ] [ arg ] [ as ] [ at ] [ b ] [ ba ] [ be ] [ ch ] [ char ] [ character ] [ co ] [ code ] [ com ] [ comma ] [ command ] [ dd ] [ de ] [ du ] [ ed ] [ eh ] [ er ] [ era ] [ es ] [ fi ] [ file ] [ filter ] [ flag ] [ fo ] [ for ] [ fr ] [ gr ] [ gu ] [ h ] [ handle ] [ hat ] [ hidden flag ] [ hr ] [ id ] [ il ] [ in ] [ input ] [ int ] [ interactive ] [ interface ] [ interrupt ] [ io ] [ iq ] [ is ] [ it ] [ J ] [ Jargon File ] [ la ] [ lag ] [ ld ] [ Lex ] [ lt ] [ ma ] [ man ] [ mm ] [ mo ] [ mod ] [ mode ] [ module ] [ na ] [ ng ] [ ni ] [ no ] [ norm ] [ np ] [ ns ] [ om ] [ op ] [ ph ] [ pr ] [ process ] [ processing ] [ program ] [ pt ] [ query ] [ rc ] [ re ] [ ro ] [ ru ] [ sa ] [ say ] [ se ] [ sh ] [ si ] [ sit ] [ so ] [ st ] [ switch ] [ T ] [ tc ] [ text ] [ th ] [ to ] [ tr ] [ ua ] [ up ] [ us ] [ ve ] [ write ]