Related Clues:

• Sentence subject, often
• What a spy may write in
• It may be a common object
• Program lines
• Verb preceder, usually
• Common object, maybe
• Java ingredient?
• A common subject, maybe
• Word that's an example of itself
• Something to crack
• Set of rules
• Morse __
• See 21 Across
• Word with bar or zip
• It might be proper