PC Ownership Versus Control
When running a campaign with a Patron account and content sharing, there are two important aspects to consider for each PC in the campaign. The first is ownership, and the second is control. In a campaign without content sharing, all PCs are owned and controlled by the respective players. All other cast members (NPCs) are owned by the campaign and controlled by the GM. When content sharing is enabled, though, these behaviors become malleable for PCs.
Ownership
The owner of a PC dictates various fundamental operations on that PC, such as retiring it, trashing it, transferring ownership, etc. More importantly, the owner determines which content can be used by the PC1. When a player owns a PC, the PC can make use of whatever content has been purchased by that player. When content sharing is enabled, PCs can instead be owned by the campaign, which allows a PC to draw upon all the content possessed by the campaign owner.
In a campaign with shared content, the player chooses whether the PC is owned by the player or the campaign during its creation. That choice then restricts what content is accessible to the PC.
After a PC is created, its ownership can be transferred back-and-forth between the campaign and players. If a player wants to take advantage of the content shared within the campaign, the player can assign ownership of their PC to the campaign. Ownership can also be assigned from the campaign to a player, and you can freely transfer characters back and forth at any time. Unsurprisingly, only the current owner of the PC can transfer its ownership - it can never be taken away by another user.
Whenever ownership is transferred, the new content access rights are immediately applied to the character. If the new owner lacks content that was already in use by the PC, the corresponding aspects of the character immediately become disabled - but not deleted. If the character is then transferred to a new owner, the available content may change again. Based on the content available to the new owner, more character options may become disabled and others may be re-enabled (possibly some of each). And if the current owner purchases the disabled content, those options will immediately become enabled once again.
The fact that character options merely become disabled and not deleted is critically important. This approach makes it possible for a player to migrate their character from one campaign with content sharing to another without losing anything in the process. Aspects of the character become disabled when removed from the first campaign, and appropriate aspects are immediately re-enabled when the character is introduced into the second campaign - depending upon the content available in the second campaign, of course.
Control
The question of control comes into play when PCs are owned by the campaign and content sharing is enabled. The whole point of content sharing is that the players manage their own PCs, even though they are owned by the campaign, and that's exactly what being the controller provides. Each PC has exactly one controller assigned at any point in time, which will typically be the player running the PC.2
An important distinction from ownership is that control is granted solely by the owner of a PC. This means that the campaign owner can take control of a PC away from a player at any time. The assumption is that GMs will only do this with good reason, but that can't be guaranteed. Consequently, certain safeguards are in place for players when control is assigned, and those are outlined in the caveats section below.3
The ability for the campaign owner (GM) to take control can be quite handy at times. For example, GMs can more directly help a new player put together their PC, since the GM can take control, make changes to the character, and then give control back to the player. Another convenient situation is when a player is unable to make it to a game session. If the PC is owned by the campaign, the GM can take control during the session and manage the character on behalf of the player, as needed. Alternatively, the GM could transfer control of the PC to another player in the group, having that player manage the character for the session. Enterprising groups will likely find plenty more situations where temporarily transferring control of PCs can be extremely beneficial. Just remember to acquire permission from the PC's original controller.
Caveats
1. Content sharing derives from the campaign owner and not the GM. Currently, the campaign owner and GM are the same user, but we plan to allow the GM role to be assignable by the campaign owner in the not-too-distant future. At that point, this distinction will become critical, since the campaign member providing the shared content for everyone will no longer need to be the GM, and even the GM can draw upon the resources purchased and shared by the campaign owner.
2. There are a few actions on characters that are exclusively the domain of the GM, regardless of ownership or control. For example, setting up initiative when entering Tactical mode is always handled by the GM, both for PCs and NPCs alike.
3. As a safeguard, whenever ownership is transferred or control is assigned away from a player, a copy of the character is automatically created for the player losing ownership/control. The cloned character is placed in the root folder of the player's independent characters outside of the campaign. This ensures that users can never fall victim to an inconsiderate GM that refuses to return a character to the original owner.
A similar behavior occurs in reverse whenever a character is withdrawn from a campaign, such as when a player drops out. A copy of the withdrawn character is always retained within the campaign. This ensures continuity for the campaign if that character is in some way key to the story. The GM can readily turn the abandoned PC into an NPC, assign the character to a different player, or whatever they deem appropriate. Meanwhile, the former player has a completely independent copy of the character that they can use elsewhere.