@Override
            public void render(final Context context, final String data, final SafeHtmlBuilder sb) {
                if (tooltipFunction != null) {
                    final String tooltip = tooltipFunction.apply(data);
                    if (data != null) {
                        if (tooltip != null) {
                            sb.appendHtmlConstant("<div title=\"")
                                    .appendEscaped(tooltip)
                                    .appendHtmlConstant("\">");
                        }
                        sb.append(SafeHtmlUtils.fromString(data));
                        if (tooltip != null) {
                            sb.appendHtmlConstant("</div>");
                        }
                    }
                } else {
                    super.render(context, data, sb);
                }
            }
A simple text cell with the value of the hover tooltip provided by tooltipFunction, which is
applied to the cell value.
stroom-core-client/src/main/java/stroom/util/client/DataGridUtil.java