Criteria for client to AP join

[Questions]

I know that the criterion for a client to choose an AP among several APs is signal strength.
Customers don't seem to believe me.
I need an official document, but I can't find it because my English and search skills are low.
Is there any official document related to this?

[balaji.bandi]

best I can provide this : ( depends on what client what NIC the have)

https://documentation.meraki.com/MR/WiFi_Basics_and_Best_Practices/802.11_Association_Process_Explained

https://docs.samsungknox.com/admin/knox-platform-for-enterprise/kbas/kba-115013403768.htm

[Leo Laohoo]

Wi-Fi Client Adapter Connection and Roaming Behavior (Intel)

[Scott Fella]

Here is another good blog to look at. The main thing to understand is client NIC come in all different brands and models, firmware also can produce uniqueness during the association process. 
http://wifinigel.blogspot.com/2015/03/what-are-sticky-clients.html?m=1

Search 802.11 roaming decisions

[JPavonM]

Yet another one from Apple:

https://support.apple.com/en-us/HT203068

HTH
-Jesus
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