A tag is shortcut to a particular node in a subtree. Tagnames are generally short, while the full path to a particular node may require a lot of typing. Tagnames may be confusing because sometimes you need to specify the subtree, but sometimes you do not. Each tagname is associated with a particular subtree. Thus, they are not necessarily globally unique, but are unique within a subtree. This is why it is sometimes necessary to qualify the tagname with the subtree that the tag belongs to. So if you only open one subtree, then you do not need to qualify the tagname. But if multiple subtrees are open, then you must qualify the tagname. For example, if you've only opened the ELECTRONS subtree, then you can use the tag \TSTE_CORE to refer to \ELECTRONS::TOP.TS.BLESSED.CORE:TEMP. However, if other subtrees are open, then it is necessary to qualify the tagname: \ELECTRONS::TSTE_CORE.