The XSF Bylaws is a document located on xmpp.org that says how the XSF as a foundation operates.
This section contains information, questions about parts of the bylaws that do not correspond to how the XSF actually operates, and could be clarified and/or updated.
It is described in the bylaws that a board quorum is established by a majority (3/5) of board members, and out of this quorum a majority (2/3) can vote a motion. That is, 2 board members can pass a vote during a meeting with 3 present.
The presence of a majority of the Members of the Board of Directors shall constitute a quorum
a vote of the majority of the Directors present at a meeting in which a quorum is present shall be the act of the Board of Directors
According to "current practices", Board will not make decisions when there are only 3 Directors present.