§1. Extensions. An "extension" is a supplementary piece of Inform 7 source text. Inform programs sometimes explicitly ask for these, with sentences like so:
Include Locksmith by Emily Short.
Their presence can also be implicitly required by the use of certain kits. For example, if BasicInformKit is used (and it always is), then the extension Basic Inform by Graham Nelson (basic_inform) is auto-included. Similarly, use of either WorldModelKit or CommandParserKit mandates the inclusion of the Standard Rules for interactive fiction (standard_rules).
The Inform GUI apps come with numerous other built-in extensions besides these two, but all are smaller and easier to read, and they are not provided as webs. See: https://github.com/ganelson/inform
§2. Kits. The middle phase of the Inform 7 compiler turns source text into a low-level abstract program in a format called inter. The final phase merges this with pre-compiled inter libraries called "kits".
Every source text needs a kit called BasicInformKit, and a kit associated with the natural language it will eventually read or write, such as EnglishLanguageKit; but then one of two things can happen:
- (a) If the user explicitly declares other kits to use, those are used;
- (b) Otherwise, WorldModelKit and CommandParserKit are used;
- (c) If neither WorldModelKit nor CommandParserKit is used, then BasicInformExtrasKit is used.
In effect, Inform by default assumes it is making an interactive fiction of some kind, and must be explicitly told if it's to make a "basic" program with no world model or command parser.
§3. Each kit is a web. Inter code is highly verbose, very low-level and not at all legible, so these webs do not contain textual Inter code: instead, they are written in Inform 6 syntax. The inter tool then converts these to binary inter code in a process called "assimilation". This means that to create or edit kits, you need to be able to write Inform 6 code, but it's a simple C-like language to learn if all you're doing is writing functions.