YAML files contained here are processed in lexicographic order, and they allow to define product properties in a efficient way.
Processing of those files can use jinja2, and macros or conditionals have access to product properties defined previously and in the product.yml.
Properties in a file are expressed in two mappings - obligatory default and optional overrides.
Properties defined in a mapping nested below default can be overriden in a mapping nested below overrides.
A property can be set only in one file, so the default-override pattern implemented by Jinja macros can be accomplished, but it has to take place in one file.
Properties specified in the product.yml can't be overriden by this mechanism, and attempting to do so will result in an error.
Conventionally, use the filename numerical prefix e.g. 10- to ensure that some symbols are available before they are used in a definition of other symbols.