Possible Clues:

• With 29-/30-Across, wiggle room ... or a hint to this puzzle's theme
• Space at edge of page
• Mother right, with mother's ruin on edge
• Border where farm animal falls over trap
• Skirt gets drink stain at the top
• -- of error
• Spoil drink for profit
• Space along the page border
• Place for editing marks
• That'll spoil just the edge of your drink