Injector

An Injector (in-jack-tor) is a statement that belongs to a Jack Tree but does not follow Jack format (verb + noun, action statement). “Belongs” means it meaningfully adds to a particular node of the tree. There are two types of Injectors: Rules and Reference.

• Rules — business rule, business logic, regulation, with examples
• Reference — direct quote, dependency, reference data, re-use, with examples

Injectors are attached below the node they affect. A node may have one or several — unlike Jacks, an Injector does not need to follow the “two or more” rule. An Injector can be multi-line or multi-value, which is especially common for Specifications.

Injectors exist so a Jack can stay a pure action statement. Context that isn’t itself an action — a constraint, a source, a piece of background — still needs to live somewhere on the tree, but folding it into a Jack’s wording would break the verb+noun format and make that Jack harder to test. An Injector carries that context without diluting the Jack it’s attached to.

A quick way to tell them apart: if a statement can stand alone as a verb + noun action, it’s a Jack, not an Injector — regardless of how it’s currently worded. Rules and Reference serve different roles too: a Rule typically constrains or validates the node it’s attached to, while a Reference typically informs or traces it back to a source. Mixing the two under one Injector is a common early mistake worth watching for.