if 0 {I've come across skepticism about [Tcl]'s facility for bit manipulation one too many times.
While [RS]'s usual ''tours de force'' such as "[Playing with bits]" and "[Big bitstring operations]"
show how '''good''' Tcl can be at bit manipulation, this page has a far more limited ambition:
simply to help hardware- or [C]-oriented developers to feel comfortable working on low-level
data in a higher-level language.}

      # Let's experiment:  one model for "low-level data" is a byte array, or
      # byte sequence.  A sequence of eight-bit values is often the manifestation
      # of information received from a physical device through a serial port, or
      # from a remote host through a network connection.  Start, then, with
      # sample data, a sequence of seven eight-bit quantities.
  set sample \x63\x77\x54\x00\x83\x41\x42
      # While they're all there, only some are displayable.
  puts $sample
  
      # Let's make a utility that'll show the content of a byte
      # sequence as hex data:
  proc show byte_sequence {
    binary scan $byte_sequence H* x
    puts [regsub -all (..) $x {\1 }]
  }

       # Display our sample data.
  show $sample

      # Suppose bits 3 and 4 combine to make some type specification.
      # Let's look at them:
  foreach byte [split $sample {}] {
    puts "The type of this byte is '[expr 0x06 & [scan $byte %c]]'."
  }

       # We can "mask off" unwanted bits.
  foreach byte [split $sample {}] {
      puts "After masking, we're looking at '[format %2X [expr 0x3F & [scan $byte %c]]]'."
  }

  ################################################################

      # This sample datum is of five sixteen-bit quantities.

  # Still to come:  (sixteen-bit) word data, and its management.
  # Also:  remarks on RE (string trim; (..?)).