How do milestones work for rules of type Reaction is given?

[ptprog]

When using a rule of type "Reaction is given", what is the meaning of the milestone?

For example, if we set it to "It is their 10th reaction", will the rule be applied: When a specific post receives the 10th reaction?  When a user receives the 10th reaction considering all posts?  When a user gives the 10th reaction considering all posts? Other?

In other words, is the milestone for the user giving the reaction, or for the receiving user?  And do we count the reactions on a specific post, or for all posts?  (I actually think all the variants should be supported, but for now I'm wondering which one is currently implemented.)

[Dexter_X]

According to support, the milestone is always for the receiver : the 10th reaction is the 10th reaction received by a user in the whole community (except if you have filtered by forum or by reaction type).
You cannot define rules with milestones for the "giver".