I ran into this limitation on e.g. bug 31503. I want to add locations that match authorised values for category CONSENT_TYPE. But Koha only allows a selected set of locations for html blocks. If we could allow picking a field from the combo or typing free text, we provide more flexibility in the use of this feature. Obviously this triggers a development discussion on field names. We have category, location and code. And their use becomes a bit unclear. Category is the most clear one. Although html and pages are quite similar. Location is opac or staff etc. for news and pages. But is used as a kind of block name for html_customizations. Code is used to group the records for default and translated languages for an item in all categories. The name is rather obscure. While describing this, bug 31383 comes to mind again..