bidi - Unicode Bidi Algorithm (UBA) Demo
Type in the sample text, and hit "Show Bidi". Below, you'll see how the rules in the UBA are applied to the characters. Clicking on any character class (like "EN") will show the Unicode characters with that property value. Clicking on a rule (like "W5") will take you to the rule in the UBA spec.
If you turn on "ASCII Hack", then ASCII characters in the sample will be interpreted as if they were Arabic, Hebrew, etc. for the purpose of illustration.