Shared string to string maps stored as TOML files, used for transliteration from one script to another.
Example users: sanscript.js and indic_transliteration_py.
- The schema definition implicitly specifies a default (with possible alternates). So, we have itrans as well as itrans_lowercase.
- Currently we don't support inheritance and overriding of schemas - so there exist related copies like itrans and itrans_dravidian.