Usually, ESL updates (redraws) the screen after all the statements in a response definition have been executed, in order to optimize performance; for example:

 

response to Go

    make object green

    make object red

    make object green

 

When ESL executes this response, the user will never see Go as red. But if you use the wait 0 statement in between color changes, ESL will update the screen immediately, even though all the action statements in the response have not finished executing. Building on the above example, if you specify wait 0 after each of the first two color changes:

 

response to Go

    make object green

    wait 0

    make object red

    wait 0

    make object green

 

you will see Go flash green, red, and back to green.