Question: how do i add legends to a multi-animation plot

i am modeling a simple standing wave. i have created three plots y1, y2 and y and then i am using animate to move them. the problem is that i cant add a legend describing every plot and i am not getting how to do this.

in addition when i click on the plot and then go to the legend menu, both show legend and edit legend are disabled.

here is my code
 
with(plots): y1:=0.01*sin(Pi/2*x-40*Pi*t);

y1 := -0.01 sin(-1/2 Pi x + 40 Pi t)

> y2:=0.01*sin(Pi/2*x+40*Pi*t);

y2 := 0.01 sin(1/2 Pi x + 40 Pi t)

> y:=y2+y1;

y := 0.01 sin(1/2 Pi x + 40 Pi t) - 0.01 sin(-1/2 Pi x + 40 Pi t)

> animate(plot,[y1,x=0..10,legend="testing"],t=0..5,frames=50);
testing is not displayed on the plot
 
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