unify structure info.

docs/scarpet/api/BlocksAndWorldAccess.md

@@ -532,13 +532,17 @@ Returns spawn potential at a location (1.16+ only)
 Checks wordgen eligibility for a structure in a given chunk. If no structure is given, or `null`, then it will check
  for all structures. If bounding box of the structures is also requested, it will compute size of potential
   structures. This function, unlike other in the `structure*` category is not using world data nor accesses chunks
-  making it preferred for scoping ungenerated terrain.
+  making it preferred for scoping ungenerated terrain, but it takes some compute money to calculate the structure.
+  
+  Unlike `'structure'` this will return a tentative structure location. Random factors in world generation may prevent
+  actual structure from forming.
   
 If structure is specified, it will return `null` if a chunk is not eligible, `true` if the structure should appear, or 
-a pair of coordinates indicating bounding box of the structure.
+a map with two values: `'box'` for a pair of coordinates indicating bounding box of the structure, and `'pieces'` for 
+list of elements of the structure (as a tuple), with its name, direction, and box coordinates of the piece.
 
 If structure is not specified, it will return a set of structure names that are eligible, or a map with structures
-as keys, and pair of bounding box coordinates as values. An empty set or an empty map would indicate that nothing
+as keys, and same type of map values as with a single structure call. An empty set or an empty map would indicate that nothing
 should be generated there.
 
 
@@ -548,7 +552,8 @@ Returns structure information for a given block position. Note that structure in
 blocks from the same chunk. `structures` function can be called with a block, or a block and a structure name. In 
 the first case it returns a map of structures at a given position, keyed by structure name, with values indicating 
 the bounding box of the structure - a pair of two 3-value coords (see examples). When called with an extra structure 
-name, returns list of components for that structure, with their name, direction and two sets of coordinates 
+name, returns a map with two values, `'box'` for bounding box of the structure, and `'pieces'` for a list of 
+components for that structure, with their name, direction and two sets of coordinates 
 indicating the bounding box of the structure piece.
 
 ### `structure_references(pos), structure_references(pos, structure_name)`