code: function release_simulated_altgr(keysym) {
  
          // Both Ctrl+Alt must be pressed if simulated AltGr is in use
          if (!guac_keyboard.modifiers.ctrl || !guac_keyboard.modifiers.alt)
              return;
  
          // Assume [A-Z] never require AltGr
          if (keysym >= 0x0041 && keysym <= 0x005A)
              return;
  
          // Assume [a-z] never require AltGr
          if (keysym >= 0x0061 && keysym <= 0x007A)
              return;
  
          // Release Ctrl+Alt if the keysym is printable
          if (keysym <= 0xFF || (keysym & 0xFF000000) === 0x01000000) {
              guac_keyboard.release(0xFFE3); // Left ctrl 
              guac_keyboard.release(0xFFE4); // Right ctrl 
              guac_keyboard.release(0xFFE9); // Left alt
              guac_keyboard.release(0xFFEA); // Right alt
          }
  
      }
docs: Releases Ctrl+Alt, if both are currently pressed and the given keysym
  looks like a key that may require AltGr.
  
  @private
  @param {Number} keysym The key that was just pressed.