Ambiguity of multi-license notation

If a package is released under the terms of two licenses the manual says

Multiple licenses should be separated by commas, Example: GPL-3.0-or-later, custom:Hugware.

However, this does not make it clear whether either of the license terms apply, or whether both apply. An example of a package where both licenses apply is picom which is under the terms of both the MPL-2.0 and MIT licenses.

This ambiguity could be avoided by using SPDX expressions to combine multiple licenses. These expressions can be arbitrarily complex and cover combinations of licenses (AND and OR) as well as exceptions (WITH) and grouping with parentheses. In the case of picom the SPDX expression is MPL-2.0 AND MIT. In fact, there is an SPDX file in the repo that contains this license: https://github.com/yshui/picom/blob/197b4bd396590cb5df61eb54ec6a1dadf1115a5d/LICENSE.spdx