## @abstract the read is paired in sequencing, no matter whether it is mapped in a pair 
BAM_FPAIRED       =1
# the read is mapped in a proper pair 
BAM_FPROPER_PAIR  =2
# the read itself is unmapped; conflictive with BAM_FPROPER_PAIR 
BAM_FUNMAP        =4
# the mate is unmapped 
BAM_FMUNMAP       =8
# the read is mapped to the reverse strand
BAM_FREVERSE      =16
# the mate is mapped to the reverse strand
BAM_FMREVERSE     =32
# this is read1
BAM_FREAD1        =64
# this is read2
BAM_FREAD2       =128
# not primary alignment
BAM_FSECONDARY   =256
# QC failure
BAM_FQCFAIL      =512
# optical or PCR duplicate
BAM_FDUP        =1024
