This is how I could see tags working: Add a "Layer Tags" panel.  Layer tags are named, in a flat namespace (no hierarchy needed), and global to the entire document (independent of spread or artboard). Any given layer can have one or more tags associated with it.  A layer which has one or more tags associated with it would show a tag icon in the Layers panel, and the tag icon would be a different color when that tag is selected in the Layer Tags panel, to help identify which layers are associated with a given tag.  Clicking on the tag icon in the Layers panel would select the tag(s) that layer belongs to in the Layer Tags panel. The Layer Tags panel would have buttons underneath the list of tags to "Create Tag from Selection", "Add Tag(s) to Selected Layers", "Remove Tag(s) from Selected Layers", "Delete Tag(s)", and "Delete Tag(s) and the Layers Tagged With Them", etc...  maybe that last one should be in a context menu or something instead as it is relatively dangerous. Next to each tag within the list in the Layer Tags panel would be three icons: one would select all layers in the current spread or artboard which are tagged with that tag, one would be a visibility toggle for the tag (eye icon), and one would be a lock toggle for the tag. A layer which is tagged would be visible if it meets the existing visibility requirements AND at least one of its tags is set to visible. A layer which is tagged would be locked if the current locking rules would indicate it is locked OR at least one of its tags is set to locked.   Build on this by adding tags to the export persona (the way layers can be used there now), etc.   Note that this is not a complete replacement for the concept of global layers.  Global layers would impose front-to-back ordering of their contents and force a structure to the document as a layer could only be a member of one global layer at a time, while multiple tags could apply to a given layer and the layers having those tags could be all over the place in terms of z-order.     Strange bonus idea: adding adjustment layers to tags.  These adjustments would be applied to each layer having that tag, across the entire document.  Not sure if this would be practical or not, or even genuinely useful, but it is a potentially interesting thought so I'm adding it here anyway.