        function setupCanvases() {

            // Make sure the placeholder is clear of everything except canvases
            // from a previous plot in this container that we'll try to re-use.

            placeholder.css("padding", 0) // padding messes up the positioning
                .children().filter(function() {
                    return !$(this).hasClass("flot-overlay") && !$(this).hasClass('flot-base');
                }).remove();

            if (placeholder.css("position") == 'static')
                placeholder.css("position", "relative"); // for positioning labels and overlay

            surface = new Canvas("flot-base", placeholder);
            overlay = new Canvas("flot-overlay", placeholder); // overlay canvas for interactive features

            ctx = surface.context;
            octx = overlay.context;

            // define which element we're listening for events on
            eventHolder = $(overlay.element).unbind();

            // If we're re-using a plot object, shut down the old one

            var existing = placeholder.data("plot");

            if (existing) {
                existing.shutdown();
                overlay.clear();
            }

            // save in case we get replotted
            placeholder.data("plot", plot);
        }
The software constructs all or part of an SQL command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended SQL command when it is sent to a downstream component.