What is the difference between how browsers implement POST and PUT requests?

when learning REST, I learned that POST requests are non-idempotent, while PUT requests are idempotent, so POST is suitable for adding and PUT is suitable for modification.
there is a question here, is the idempotency here just a difference in definition? Is there any difference in browser behavior when sending POST and PUT requests, especially in case of a failed retry? If it"s just a difference in definition, then idempotent or not is entirely implemented by programmers on the server side (that is, it is possible to implement POST as idempotent and PUT as non-idempotent). Is that correct?

Put post restful rest

Mar.07,2021

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MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1e90ab2-68a66.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1e90ab2-68a66.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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