They store plain-text data representing object names, 3D coordinates (X, Y, Z axes), rotation matrices, scale, and placement flags.
If you import a ydd or ydr file and it looks fine, but is stretched in OpenIV, this is usually an export setting issue within Blender. Xml To Ydr LINK
If your tool refuses to build the output file or causes the game/FiveM client to crash on launch, look out for these common issues: They store plain-text data representing object names, 3D