in standar SEO (Search Engine Optimization) Effect for Word with Bold, italic, underline, is an important aspect to the sensitivity of an article. the color of a letter (accesories fonts) may be influential as well. In addition, meta keywords and meta description is another part that is useful to improve sensitivity.
It depends on the content and links to an article that was written well. increasingly in an article and knick knacks that exist in a content could increase the sensitivity.
Searches are not case sensitive whether for Yahoo or Google. Its not like its a password or something.