what's the meaning of tag "a":

[xiexr]

for example:
S utg000001l * LN:i:41537
a utg000001l 0 m54136_170926_195115/39518486/15846_38527:2064-21507 + 3960
a utg000001l 3960 m54061_170914_081333/37748951/9612_35354:3-15698 + 7

each colum represents what?

[sjackman]

The lower case a record is a non-standard application specific record type, so it's not covered by this specification. I believe those a records are output by https://github.com/lh3/miniasm so, @lh3 would know the answer. My best guess is that the a records specify where the reads are placed in the unitigs.