Define a meter to be used as a "container" for the "contents" of another meter.
The documentation and a bunch of examples for Container are at https://docs.rainmeter.net/manual-beta/meters/general-options/container/
The intent of this is two-fold:
A meter that has a Container option will in effect be put "inside" the container meter. It will be positioned relative to the container, and will be visibly constrained by it. Only the part of the content that is "inside" the container will be drawn.
Think sliding content, a menu or launcher for instance, into view without needing to start outside the entire skin.
The content will be "masked" into any solid pixels in the container meter. So only the part of the content that is masked into a "solid" pixel in the container will be drawn.
Think masking an image into a String meter, or an image into a Shape meter.
An existing discussion about this feature is at https://forum.rainmeter.net/viewtopic.php?f=123&t=30121#p155025.
The beauty of Container is the simplicity of the concept.
- Content meters are "constrained" by the W and H boundaries of the container.
Content outside the container is not drawn, and in effect doesn't exist.
- Content meters are only drawn on solid pixels of the container.
Any transparency of both the container and the content are cumulative.
- The first content meter in a container is automatically relative to the top left of the container.
"r" and "R" are ignored.
- Subsequent content meters in a container are relative to each other.
"r" and "R" are functional.
- Meters that are not content are relative to the immediately preceding meter that isn't content.
- Containers may not be "nested".
As with all the best features, this is very simple in principle, and very easy to wrap your head around, while being VERY powerful and flexible, and allowing for a lot of creativity. Go nuts!