One way you could do this is to make a very long text area and embed it into a more reasonable sized panel. You might have to use a userlib SendMessage command to keep the cursor on screen tho.
window=CreateWindow( "Simple syntax highlighting text editor",0,0,640,480 )
;textarea=CreateTextArea( 0,0,ClientWidth(window),ClientHeight(window)-96,window )
textareapan=CreatePanel( 0,0,ClientWidth(window),ClientHeight(window)-96,window )
textarea=CreateTextArea( 0,0,ClientWidth(window),3000,textareapan )
SetGadgetLayout textarea, 1,1,1,1
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