def print_help
@output.puts "<div style=\"display: none;\" id=\"help\">\n<img src=\"empty.png\"> Enter a decimal value <i>d</i> into the threshold field and click \"Apply\"\nto hide all nodes marked with time values lower than <i>d</i>.<br>\n<img src=\"empty.png\"> Click on \"Expand All\" for full tree expansion.<br>\n<img src=\"empty.png\"> Click on \"Collapse All\" to show only top level nodes.<br>\n<img src=\"empty.png\"> Use a, s, d, w as in Quake or Urban Terror to navigate the tree.<br>\n<img src=\"empty.png\"> Use f and b to navigate the tree in preorder forward and backwards.<br>\n<img src=\"empty.png\"> Use x to toggle visibility of a subtree.<br>\n<img src=\"empty.png\"> Use * to expand/collapse a whole subtree.<br>\n<img src=\"empty.png\"> Use h to navigate to thread root.<br>\n<img src=\"empty.png\"> Use n and p to navigate between threads.<br>\n<img src=\"empty.png\"> Click on background to move focus to a subtree.<br>\n</div>\n"
end