Possible Clues:

• Spelling Bee feature
• 'The quick brown fox jumps over the lazy dog', for example
• It's complete from A to Z
• Greek airline no longer stores A to Z in this
• Sentence containing all 26 letters
• A 'perfect' one uses all 26 letters once each, as seen in four answers in this puzzle
• Pam rang excitedly — “This includes every letter!”
• “Crosswords are just very fun mini-quizzes with packaged little boxes,” e.g
• Puzzle that uses every letter
• 'Mr. Jock, TV quiz Ph.D., bags few lynx,' for example