support word transcriptions

[dwhieb]

Use the \w code for this.

Rarely needed, since in principle this line would be exactly the same data as the \txn line, with only differences in spacing (though this is still useful).

This line should not contain morpheme breakdowns.

This line may be in multiple orthographies.

Clarify that this line often has extra white space for the purpose of vertical alignment, while the utterance transcription line does not.