Describe the feature
When you create several controlers, for example several siemens S71500 devices, and there are the same tags names inside them, a problem is raised with $getTagId('Tag name');, because the device is not an argument for the function. This could be addressed giving different tags names for vars inside every device. I didn't test the scope of this issue in other functions who works with IDs.

Describe the solution you'd like
May be giving a "device" argument to that function -> $getTagId('Tag name', 'device');