XML in 1 minute

XML defines a document structure and a vocabulary

  <list>
    <item>First item</item>
    <item>Second item</item>
  </list>

Chemical Markup Language for Nitrogen Dioxide (^.O-N=O)

<molecule id="no2">
  <atomArray>
    <atom id="n1" elementType="N" hydrogenCount="0"/>
    <atom id="o1" elementType="O" hydrogenCount="0"/>
    <atom id="o2" elementType="O" hydrogenCount="0"/>
  </atomArray>
  <bondArray>
    <bond id="bo1" atomRefs2="n1 o1" order="2"/>
    <bond id="bo2" atomRefs2="n1 o2" order="1"/>
  </bondArray>
</molecule>

...and briefer...

<molecule id="no">
  <atomArray atomID="n1 o1 o2" 
    elementType="N O O" hydrogenCount="0 0 0"/>
  <bondArray atomRef1="n1 n1" atomRef2="o1 o2" order="2 1"/>
</molecule>