See the references relating to the robot exclusion standard in the WebSTAR section of the StarNine Technical Notes page. If you have used one of these to create your site, be prepared to have to fix links that aren't correct. Image maps may not work, and you may encounter other problems. Some of them create documents that can be easily edited in html source, others don't have editing of source available within the application or create such complex table structure that it is difficult to figure out the structure. If you plan to run a web site, and especially if you plan to host sites for other people, you will need to learn html - or have someone available to troubleshoot problems in the code of pages served at your site.
Different browsers respond differently to html syntax errors.
Some will handle things more gracefully than others.