Here are the classes, structs, unions and interfaces with brief descriptions:

gtksourceview::SourceBuffer	Buffer object for SourceView
gtksourceview::SourceCompletion	Main Completion Object
gtksourceview::SourceCompletionContext	SourceCompletionContext
gtksourceview::SourceCompletionInfo	Calltips object
gtksourceview::SourceCompletionItem	SourceCompletionItem
gtksourceview::SourceCompletionProposal	Completion proposal object
gtksourceview::SourceCompletionProvider	Completion provider interface
gtksourceview::SourceCompletionWords	Words completion provider
gtksourceview::SourceGutter	Gutter object for SourceView
gtksourceview::SourceIter	An iterator type for SourceBuffer
gtksourceview::SourceLanguage	Object representing a syntax highlighted language
gtksourceview::SourceLanguageManager	Class which provides access to SourceLanguages
gtksourceview::SourceMark	Mark class for SourceBuffer
gtksourceview::SourceMarkup	It is just a class holding markup string
gtksourceview::SourcePrintCompositor	Compose a SourceBuffer for printing
gtksourceview::SourceStyle	Class representing a style
gtksourceview::SourceStyleScheme	Object controlling apperance of SourceView
gtksourceview::SourceStyleSchemeManager	Class providing access to SourceStyleSchemes
gtksourceview::SourceUndoManager	Undo manager interface for SourceView
gtksourceview::SourceView	The view object