public Builder<T> displayType(final DisplayType displayType) {
            this.displayType = displayType;
            return this;
        }
@param showIcon         Set to true to show the type icon next to the text
@param cellTextFunction Function to provide the cell 'text' in HTML form.
@param docRefFunction   Function to provide a doc ref if the value can give us one.
@param cssClassFunction Function to provide additional css class names.
stroom-core-client/src/main/java/stroom/data/client/presenter/DocRefCell.java