SA tags with a position of -1

[ernfrid]

I've seen this twice now where Lariat aligned BAMs contain alignments where the SA tag reports a position of -1. (For an example, see hall-lab/extract_sv_reads#8). My expectation was that the position in the SA tag is 1-based, although the specification is not explicit on this point. For BWA-MEM aligned BAMs, I've never encountered a negative position in this tag.

Since it's unclear to me, I thought I'd open an issue to ask what a position of -1 means in the SA tags for Lariat aligned BAMs?

Thanks in advance.