solid
Returns: Boolean
An instance can be flagged as solid through the object properties, or by changing the value of this variable. If solid is true, a special collision event is generated whereby the instance
is returned automatically to the position it was at in the step previous to the collision. If it is set to false, all collisions must be dealt with through the collision event.
with (object_index)
{
solid = !solid;
}
The above code checks the "solid" flag of all instances that have the same object_index as that which is running the code and if "solid" is false it is changed to true.