Possible Clues:

• Observer's editor only partly shows experience
• Is well informed about metric composition
• Acquainted (with) - up (on)
• Thoroughly acquainted with what poet wrote on day one
• Thoroughly acquainted with and skilled in something
• Up on, with 'in'
• Having knowledge, skilled - in poetry?
• Experienced in or having knowledge of
• Thoroughly acquainted poetically?
• Some are clever, sedulous and learned