Possible Clues:

• Quartet depart endless hosts to finally play for one
• It's frowned upon by some purists but one is to happily cohabit
• The answer is to be finally solved, for example
• ''To boldly go,'' for example
• "To boldly go," e.g
• 'To boldly go,' e.g
• Grammarian’s gripe, and a hint to the circled words
• Feature of "To boldly go where no one has gone before!"
• Construction to suddenly crumble for example?
• 'To boldly go where no man has gone before,' e.g.