- clips many symbols that typically only appear inside the cave passage (unless '-outline none' is set),
In case -outline none Therion is not able to decide which part of symbol (let’s say block) to clip off. But on other hand if there is not -clip off there the symbol (block) will be not appeared.
- are used by the scrap join algorithm to decide which line ends to join (for visible wall lines only),
For automatic scrap join algorithm. But you may join any kind of lines at any line points - typically wall to corner of block.
m.s.