flowchart LR
  Start[Start]
  Stop[Stop]
  Start --> Upper{{<tt>A</tt>..<tt>F</tt>}} --> Stop
  Start --> Lower{{<tt>a</tt>..<tt>f</tt>}} --> Stop
  Start --> Digit{{<tt>0</tt>..<tt>9</tt>}} --> Stop

  style Start fill:#44E
  style Stop fill:#E44