
Broken Geometry

+  unclosed sectors
+  sectors with ceil_h < floor_h

+  linedefs without a right side
+  zero length linedefs

+  linedefs which directly overlap (share a pair of vertices)
+  linedefs which partially overlap / cross over  [ties in with unclosed logic]

+  vertices at same location


Things

+  things stuck in walls or each other
-  things in the void
+  no player 1 start
-  no player 2/3/4 start  (merely show it)
-  no deathmatch starts   (merely show it)


Texturing

-  missing textures on solid walls
-  mid-masked textures on solid walls

-  valid flat names in sectors
-  valid texture names in sidedefs


Miscellaneous

-  one-sided lines without IMPASS flag   [FIX]
-  two-sided lines without 2S flag       [FIX]

-  unused vertices  [REMOVE]
-  unused sidedefs  [REMOVE]
-  unused sectors   [REMOVE]

-  sidedefs used on multiple lines (or same line twice)  [UNPACK]

?  linedef with tag but no matching sector
?  sector with tag but no matching linedef

?  list of used tag numbers

