I tried to look for the definition of “member of the alliance” but I could not find any here or on the website.
The wiki makes use of the following expressions: member of the public; working group member, forum member.
I realize that membership is not well-defined, therefore the membrane of IoP is not explicitly delineated. Perhaps contributors to IoP have their own ideas about membership and perhaps there is an implicit shared definition.
Now I am very confused myself 
Am I a member of the IoP Alliance? Can I call myself a member of a working group, for example of the Governance Task Force? I am contributing to Governance, am I a member of this working group? What’s the threshold / requirement to become a member?
I think I am definitely a member of the forum, I am active here.
I’d like opt in for the Governance TAsk force with this comment, but nowhere I can see is this would be acceptable by the rest of the community, because I haven’t fully accessed the implicit shared knowledge of the group.
No need to answer here… we will certainly address this in the Process to design governance. Membrane / Membership and other important things are part of the Governance Canvas.