Maybe we just want a subtitle type with the emissions e.g. instead of emit(sub) do emit(TEXT_SUBTITLE, sub) or emit(TEXT_CCAP, sub).
+Try "bitmap" for bitmapped text and "plain" for actual text?
+
+Should we try to preserve project back-compatibility here (i.e. do we change XML tag names...)
+on the one hand, it's just names, on the other hand...
+
+Content needs a list<TextContent> since DCP content may have multiple bits.
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