Possible Clues:

• For example, a superlative noteworthy type that's 100 per cent correct
• Like an outstanding mail carrier?
• No need for a prompt on stage if this character gets tense
• Having one's part accurately memorised
• (Of an actor) having learnt a role exactly
• Learn off by heart - you'd expect that from the postman
• Accurate in every detail
• Correct in every detail — ferret pelt etc (anag)
• What an actor should be is faultless in spelling