Question about @value substitution

Can someone point me to the code that does the substitution of @parameter values? It seems straightforward when we have something in a select SQL string like this:

            WHERE lc.course_id=@CourseId

The @CourseId is replaced with the respective value passed in via our anonymous object - all good.

But what about more complex SQL where it itself is using @parameter syntax ? for example this is the start of a quite involved query that is ultimately a SELECT:

            DECLARE @LearnerID VARCHAR(20) 

            SET @LearnerID = '{0}' 

            DECLARE @EndDate DATETIME 

            SET @EndDate = Cast((SELECT TOP 1 loa_finish_date AS LOAEndDate 
                                 FROM   learner_loa 
                                 WHERE  learner_id = '{1}' 
                                        AND approval_status = 1 
                                 ORDER  BY loa_approval_date DESC) AS DATETIME) 

How does dapper analyze this to separate user defined replacement values from other SQL declarations and assignments that also use @name syntax?

No file or test is named, and the issue asks for an explanation rather than a code change. Start by locating Dapper’s parameter-binding entry point and tracing how anonymous-object values are handled alongside SQL variables; done means documenting that distinction clearly with an example covering the shown DECLARE and SET statements.