/zone\s+"([^"]+)".+masters\s+{\s*([^}\s]+)\s*}/s
      ^ ^   ^   ^          ^   ^     ^     ^   ^
      | |   |   |          |   |     |     |   |
      | |   |   |          |   |     |     |   + - Treat string as single line
      | |   |   |          |   |     |     + - 0+ whitespaces
      | |   |   |          |   |     + - Match anything that's not } or a whitespace
      | |   |   |          |   + - 0+ whitespaces
      | |   |   |          + - 1+ whitespaces
      | |   |   + - End quotation
      | |   + - Match anything that's not a "
      | + - Begin quotation
      + - 1+ whitespaces