I’m not into OEF…but with canvasdraw you can include as many textareas / inputfields (even in mathml) as you like.
They will be embedded in the canvas.
Just use a canvasdraw command like ‘input x,y,size,readonly,value
to place the inputfield on location (x:y)
Canvasdraw command ‘inputstyle some_css_string’ may be used to adjust the inputfield looks.
Canvasdraw command ‘replyformat int’ may be use to format the output of ‘read_canvas()’ to suit your ‘answertype’
etc etc etc