gaps	AB--CD-EFG-HIJ
seq 	ABCDEFGHIJ

beginPosition(gaps)        == 0
endPosition(gaps)          == 10
clippedBeginPosition(gaps) == 0
clippedEndPosition(gaps)   == 14

gaps	-CD-EFG
seq 	CDEFG

beginPosition(gaps)        == 2
endPosition(gaps)          == 7
clippedBeginPosition(gaps) == 3
clippedEndPosition(gaps)   == 10

4 view position => 4 source position
2 source position => 1 view position

3 clipped gapped => 6 unclipped gapped
6 unclipped gapped => 2 clipped gapped

3 clipped ungapped => 5 unclipped ungapped
5 unclipped ungapped => 3 clipped ungapped

3 clipped gapped => 2 clipped ungapped
4 unclipped ungapped => 7 unclipped gapped
