Proposed Internet standard RFC 5147 provides a fragment identifier scheme for plain text documents, which allows reference to both ranges of characters and ranges of lines within a plain text document:
http://tools.ietf.org/html/rfc5147
DITA2Go supports the proposed href attribute syntax, and also provides PI markers to achieve the same effect. We recommend using the fragment identifiers described in RFC 5147 rather than PI markers, where it makes sense to do so.
§10.2.1 Including external code snippets with PI markers
§10.2.2 Including external code snippets with fragment identifiers