Let's start with an overview of terminology.:

• Compiling: The process of converting input in a text format, such as YAML or JSON, into OPS objects. Here we're focused on non-Python alternatives to using the standard Python interpreter to compile objects.
• Category: The base category of object to be created (engine, CV, volume, etc.)
• Builder: We will refer to a builder function, which creates an instance of a specific

Everything is created with plugins. There are two types of plugins used in the compiling subpackage:

• InstanceCompilerPlugin: This is what you'll normally work with. These convert the input text to an instance of a specific OPS object (for example, an OpenMMEngine or an MDTrajFunctionCV. In general, you do not create subclasses of InstanceCompilerPlugin -- there are subclasses specialized to engines (EngineCompilerPlugin), to CVs (CVCompilerPlugin), etc. You create instances of those subclasses. You write your builder function, and wrap in with in an instance of an InstanceCompilerPlugin.
• CategoryPlugin: These manage the plugins associated with a given features. Contributors will almost never need to create one of these. The only case in which you would need to create one of these is if you're creating a new category of object, i.e., something like an engine where users will have multiple options at the command line.

Other useful classes defined in the compiling subpackage include:

• Builder: The Builder class is a convenience for creating builder functions. It takes either a callable or a string as input, where a string is treated as a path to an object to import at runtime. It also allows takes parameters remapper and after_build, which are callables that act on the input dictionary before object creation (remapper) and on the created object after object creations (after_build).
• CategoryCompiler: This class manages plugins for a given category, as well as tracking named objects of that type. These are created automatically when plugins are registered; users do not need to create these.