In my layout xml file, I have included other layout xml file (each with a different android id).
I think the top answer misses the most important point and might mislead people into thinking the
tag creates a View that holds the include contents.
The key point is that include's id is passed to the root view of the include's layout file.
Meaning that this:
// activity_main.xml
// somelayout.xml
Becomes this:
// activity_main.xml