The model system is Minecraft’s way of giving blocks and items their shapes. Through the model system, blocks and items are mapped to their models, which define how they look. One of the main goals of the model system is to allow not only textures but the entire shape of a block/item to be changed by resource packs. Indeed, any mod that adds items or blocks also contains a mini-resource pack for their blocks and items.
In order to link code to models and textures on disk, there exists the class
ResourceLocation. One may recognize them from the registry system; however, their original purpose was to identify files on disk; they just happened to be useful as unique identifiers as well. A
ResourceLocation is a simple object composed of two
Strings: a namespace and a path. When a
ResourceLocation is represented as a plain string, it looks like
namespace:path. When a
ResourceLocation is created and a namespace isn’t explicitly given, the namespace defaults to
minecraft. However, it is good practice to include the namespace anyway.
The namespace of a
ResourceLocation in the model system represents a directory directly underneath
assets/. Usually, the namespace is the same as the modid (e.g. in vanilla Minecraft the namespace is always
minecraft). The path portion of a
ResourceLocation represents a context-sensitive path to file underneath the namespace. What the path means and where exactly it points depends on what’s using it. For example, when referring to a model, the path is normally resolved under
models, but when referring to a texture, it is under
assets/mod/models/file.json in one context but
assets/mod/textures/file.png in another. When something is described as requiring a
ResourceLocation, it will be defined what exactly the path means.
All strings related to the model system (especially
ResourceLocations) should be in snake case (meaning_all_lowercase_and_underscore_separated_words_like_this). This is enforced since Minecraft 1.11.