If you press the F12 key, you will get a window which you can use to search the html version of the manual. You can also open this window with the menu entry Help ▸ Find word in HTML help.
The HTML help window has a search area; if you type a string in that area you will be given a list of help topics that contain that string. If you choose a topic and click View, your web browser will show the appropriate page of the manual.