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Changes between Initial Version and Version 1 of Ticket #4431, comment 4

initial	v1
3	3
4	4	Sandarac changed the previous `messages.js` diff to the current proposal after a discussion on irc.
5		Since all observers have the playerID `-1`, chat handling based on playerID was conceptually broken (#3270) and replaced with player GUID parsing for private messages (thus being able to distinguish observers). The function `GetPlayerGUID` introduced r17771 utilized for that returns either the client identifier (GUID) or the empty string. In Singleplayer however, the gamesetup/session use `local` as a placeholder identifier in `g_PlayerAssignments`. I didn't want to transport this hardcoding to C++, but it is a possibility alternative to the proposal.
	5	Since all observers have the playerID `-1`, chat handling based on playerID was conceptually broken (#3270) and replaced with player GUID parsing for private messages (thus being able to distinguish observers). The function `GetPlayerGUID` introduced r17771 utilized for that returns either the client identifier (GUID) or the empty string. In Singleplayer however, the gamesetup/session use `local` as a placeholder identifier in `g_PlayerAssignments`. I didn't want to transport this hardcoding to C++, but it is a possibility alternative to the proposal (or adding a new JS only function that returns GetPlayerGUID() \|\| "local" to avoid some of the other "local" checks too).