Theory. Catalogs and documents
It is interesting to note the differences in the use of singular and plural terms when referring to Catalog and Document objects.
If you open the tree of any standard configuration, you can see that the objects in the Catalogs branch are generally named in the plural, while the objects in the Documents branch are generally named in the singular.
It may seem that when you create a Catalog configuration object you create a storage to keep the items of this catalog, whereas when you create a Document configuration object you create a template for a single specific document. This is not actually the case.
When you create a Catalog object in Designer, you name it in the plural (MaterialsAndServices). And you imply that in the database this object will store items describing specific materials and services (each item in the singular).
When you create a Document object, you name it in the singular (GoodsReceipt), even though you are creating the same sort of a storage as in the case of a catalog. Each record in that storage will describe a single document: a goods receipt (in the singular). Therefore, in Designer it would be conceptually correct to name Document objects in the plural, which would emphasize the fact that they describe a set of documents of that type (for example, GoodsReceipts).
However, human thinking is such that, when opening the Documents branch, people expect to see them listed in the singular rather than in the plural. So we end up with a situation where it is difficult to come up with an appropriate term to describe a whole set of documents of specific type (a set of records of a single type is far easier: a catalog, a chart, and so on). Therefore, the corresponding configuration object branch is named Documents, while the configuration objects created in this branch are named in the singular despite the fact that the branch actually contains descriptions of storages for various document types and each item in the branch describes the set of all the documents of a certain type.