real-time event event that a) occurs at the same time as the viewing and b) is not completely generated
      by the content Example 1 A Webcast of a live performance (occurs at the same time as the viewing and is not
      prerecorded). Example 2 An on-line auction with people bidding (occurs at the same time as the viewing). Example 3 Live humans interacting in a virtual world using avatars (is not completely generated
      by the content and occurs at the same time as the viewing). region perceivable, programmatically determined section of content Note In HTML, any area designated with a landmark role would be a region. relationships meaningful associations between distinct pieces of content relative luminance the relative brightness of any point in a colorspace, normalized to 0 for darkest
      black and 1 for lightest white Note 1 For the sRGB colorspace, the relative luminance of a color is defined as L = 0.2126
      * R + 0.7152 * G + 0.0722 * B where R , G and B are defined as: if RsRGB <= 0.04045 then R = RsRGB/12.92 else R = ((RsRGB+0.055)/1.055) ^ 2.4 if GsRGB <= 0.04045 then G = GsRGB/12.92 else G = ((GsRGB+0.055)/1.055) ^ 2.4 if BsRGB <= 0.04045 then B = BsRGB/12.92 else B = ((BsRGB+0.055)/1.055) ^ 2.4 and RsRGB, GsRGB, and BsRGB are defined as: RsRGB = R8bit/255 GsRGB = G8bit/255 BsRGB = B8bit/255 The "^" character is the exponentiation operator.