Merge pull request #4271 from aG0aep6G/remove-requirements

documentation: fix requirements of remove

std/algorithm/mutation.d

@@ -1563,11 +1563,11 @@ of the stability requirement, $(D remove) moved elements from the end
 of the array over the slots to be removed. This way there is less data
 movement to be done which improves the execution time of the function.
 
-The function $(D remove) works on any forward range. The moving
-strategy is (listed from fastest to slowest): $(UL $(LI If $(D s ==
-SwapStrategy.unstable && isRandomAccessRange!Range && hasLength!Range
-&& hasLvalueElements!Range), then elements are moved from the end
-of the range into the slots to be filled. In this case, the absolute
+The function $(D remove) works on bidirectional ranges that have assignable
+lvalue elements. The moving strategy is (listed from fastest to slowest):
+$(UL $(LI If $(D s == SwapStrategy.unstable && isRandomAccessRange!Range &&
+hasLength!Range && hasLvalueElements!Range), then elements are moved from the
+end of the range into the slots to be filled. In this case, the absolute
 minimum of moves is performed.)  $(LI Otherwise, if $(D s ==
 SwapStrategy.unstable && isBidirectionalRange!Range && hasLength!Range
 && hasLvalueElements!Range), then elements are still moved from the