diff --git a/src/viewport.cpp b/src/viewport.cpp
--- a/src/viewport.cpp
+++ b/src/viewport.cpp
@@ -1886,11 +1886,21 @@ bool ScrollWindowTo(int x, int y, int z,
 	return true;
 }
 
+/**
+ * Scrolls the viewport of the main window to a given location.
+ * @param tile    Desired tile to center on.
+ * @param instant Jump to the location instead of slowly moving to it.
+ * @return Destination of the viewport was changed (to activate other actions when the viewport is already at the desired position).
+ */
 bool ScrollMainWindowToTile(TileIndex tile, bool instant)
 {
 	return ScrollMainWindowTo(TileX(tile) * TILE_SIZE + TILE_SIZE / 2, TileY(tile) * TILE_SIZE + TILE_SIZE / 2, -1, instant);
 }
 
+/**
+ * Set a tile to display a red error square.
+ * @param tile Tile that should show the red error square.
+ */
 void SetRedErrorSquare(TileIndex tile)
 {
 	TileIndex old;