Allow for arbitrary documents to be stored with splits.
The workflow is as follows:
(1) In the "Documents" tab, documents can be created/changed/removed.
(2) In the ledger documents can be assigned to splits using a "assign documents" button.

Only references to existing files are stored by default (that is, the files are not copied). This can be changed via File->Document Storage settings for existing kmy files/databases. When creating a new file/database, the setting can be controlledin the initial file creation wizzard.