General keywords or index terms of any other kind can be tagged (by default using <rs>, but any other semantically appropriate elemt may be captured for this purpose) anywhere in the document where they appear in running text: e.g. in the Greek or Latin edition, translations, commentary, or any of the descriptive fields in the header. Depending on the needs of a particular project and any internal or external taxonomies in use, such a tag might look something like:
The above examples could be indexed using project-specific code for the purpose of generating indices, a search form, or for sorting or filtering texts. If a taxonomy is also in use, the <rs> may carry ref for the purpose of normalizing to a term in this taxonomy. In the example below, normalization is to the EDR vocabulary for materials (see Rei Material GoogleDoc):
General keywords that do not belong in any particular part of the text or supporting data of the edition may be gathered conveniently in a <keywords> element in the header. These keywords will generally be used only for purposes of search, indexing, or compatibility within a larger collection, rather than appearing in the human-readable part of the edition.
For keywords, subject terms or descriptions that apply specifically to the categorization or definition of the text, the <msContents> and <summary> may be used to contain either a list of terms or general prose description, as in the examples below: