I defied all conventional knowledge, and wrote my HTML5 site first. Now I am writing the HTML4 site and adding a script which detects old browsers. The question I have is mainly regarding web safe fonts. I am aware that it is best practice to use HTML instead of images of pretty text, for the benefit of SEO. However, since the HTML5 website exists with the HTML in the headers, I wonder if it is safe to use images to represent those headers in the HTML4 version of the site. Simply put, will my web client's indexing suffer? I feel that the HTML5 version will ensure good ranking, but I wanted to put it to the community and get an opinion.
Second question, should I create the more accessible version in HTML4 or XHTML?
Finally, is there a simpler way to make a new site backwards compatible, and still be able to make use of newer technology?
After a fair amount of research, I found that it is not so unusual to create a site in HTML5, and implement items for the purpose of graceful degradation.
At this site: spacebug.com/gracefully-detect-old-browsers-and-fallback-from-html5/, the authors recommend not using PHP user agent variables to detect browser capability. It says that there are too many user agents and that headers change, etc. Check out the link for their in-depth explanation. It offers that the right way to do it is to use javascript to check for certain capabilities. Since my purpose is to either render it in HTML5 or render it in XHTML, this makes my life pretty simple.
Once I found that javascript was the way to go, a simple Google search led me to this site: diveintohtml5.info/detect.html. This offers a number of methods for detecting browser functionality as it relates to HTML5.
For those who are not as savvy with the code, or for those who are looking for a quick solution, the second website also offers a link to modernizr.com, which is an "open-source MIT licensed javascript library that detects support for many HTML5 and CSS3 features."
So, thank you all for your input. I have learned a great deal from this experience, and I am hoping it will make everything much more user friendly and efficient.
Happy developing! Kat