html.Button: what does 'value' keyword do?

Dash Python
1

Hey guys,
I’m trying to change the text inside a button with a slider.
My understanding was that I could do it with the keyword ‘value’.

@app.callback(Output('button1','value'),
              [Input('slider1','value')])
 def changeSliderValue(value):
    buttontext = "Button 1 " + str(value) 
    return buttontext

but this doesn’t have any effect.