Разница между назначением (…, envir =…) и средой (…) =

В чем разница между присвоением значения имени в среде и установкой среды переменной? Я не мог понять этого из документации.

например:

MyTestFunc = function(x)
{
    myVal = "abcde"

    # what is this doing?  why is myVal not in the global environment after 
    # this call? I see it adds an environment attribute to the variable, 
    # but what good is that?
    environment(myVal) = globalenv()

    assign( "myVal" , myVal , envir = globalenv() )

    # this seems to copy graphics:::rect to the current environment which seems 
    # to contradict the behavior of environment( myVal ) above
    environment( rect ) = environment()

    # this seems to do the same thing
    assign( "rect" , rect , envir = globalenv() )
}

# this prints out rect, but shows <environment: namespace: graphics>!
rect