title: Are property values in CSS case-sensitive?
body: <p>I have observed that some CSS properties, like <code>font-family</code> declared with quotation marks, perhaps are case-sensitive, but all other are not... But <strong>how web-browsers and "HTML renderers" MUST interpret?</strong> Is the same in any CSS context (XML, SVG, etc.) and all other applications? <strong>What the standards say about?</strong></p>
  
  <p>Example: <em>Adobe InDesign</em> exported both, <code>font-family:'Optima Bold'</code> and <code>font-family:'optima bold'</code>. Can I "normalize to lower case" (ex. to merge similar classes)?</p>
  
  <h2>NOTES</h2>
  
  <p>References are incomplete and in conflict:</p>
  
  <ul>
  <li><p><a href="http://reference.sitepoint.com/css/font-family" rel="noreferrer">sitepoint.com/font-family</a> say "Note that font family names may be case sensitive on some operating systems"... It is valid for XHTML, it is updated with HTML5? <code>font-family</code>  is really the unique case-sensitive value?</p></li>
  <li><p><a href="https://stackoverflow.com/questions/2115157/is-it-necessary-to-use-lowercase-for-every-element-and-attribute-properties-in">Is it necessary to use lowercase for every Element and attribute , properties in css and xhtml ?</a> say indirectly "... use lowercase for every properties...", and answers not negate it.</p></li>
  </ul>
  
  <hr>
  
  <p>Comparing with  <a href="https://stackoverflow.com/a/12533957">this question/answers</a>, <strong>the point here</strong>, perhaps, can be translated to some (personal) objective considerations: </p>
  
  <ol>
  <li><p>There are a (objective!) normative (W3C spec of CSS2, CSS3, XHTML1, or HTML5) source for this answer?   </p></li>
  <li><p>"Standard <code>font-family</code> unique names" can not be case-sensitive (otherwise cease to be standard)... So, the only justifiable (by sensible arguments) properties to be case-sensitive are:</p>
  
  <p>2.1. <code>X</code> values at <code>url(X)</code>, see <code>background</code>, etc. properties;</p>
  
  <p>2.2. <code>content</code> values, <a href="http://www.w3schools.com/cssref/pr_gen_content.asp" rel="noreferrer">example</a>;</p>
  
  <p>2.3. ... <strong>more ??</strong> ...</p></li>
  </ol>