- @param mode open mode /[rw](b?)(u?)(h?)/: 'r' for reading, 'w' for
- writing, 'b' for BAM I/O, 'u' for uncompressed BAM output and 'h'
- for outputing header in SAM. If 'b' present, it must immediately
- follow 'r' or 'w'. Valid modes are "r", "w", "wh", "rb", "wb" and
- "wbu" exclusively.
+ @param mode open mode /[rw](b?)(u?)(h?)([xX]?)/: 'r' for reading,
+ 'w' for writing, 'b' for BAM I/O, 'u' for uncompressed BAM output,
+ 'h' for outputing header in SAM, 'x' for HEX flag and 'X' for
+ string flag. If 'b' present, it must immediately follow 'r' or
+ 'w'. Valid modes are "r", "w", "wh", "wx", "whx", "wX", "whX",
+ "rb", "wb" and "wbu" exclusively.