SAM tools

Is there any precedent for a SAM alignment record optional field tag 
describing the length of 3' (suffix if 0x10 in bit field is not set) 
sequence which is identified as adapter, i.e. to be hard clipped later 
or ignored by an aligner?

If not, does any one have any thoughts on using "A3" for this purpose 
(adapter  3' )?

David


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