These can provide depth and focal points to a page. I believe a good recommendation is that the code know how to determine degrees for more ease of putting values for the properties. Coders need to include all the different typesw of search engines so that all are compatible. Lastly, coder should know the different units per element used such as "deg", "px", and using no units
Too many of these on the page can be cause the page to become quite chaotic and circus-like. Coders should keep this in mind when determining how many and what will have these effect and the purpose of the paged.