[xml] XML guidelines

[Norberto Lopes <collector mail telepac pt>]

I'm having some difficulties deciding the best way to describe what I
want, being the best given by efficiency when searching the tree and
adding or removing elements.

Which one do you think is best?

1st one:
<example>
  <sum>2+1</sum>
  <sum>3*2</sum>
  <div>3/2</div>
  <div>1/2</div>
  <mult>3*5</mult>
  <mult>5*9</mult>
</example>

2nd one:
<example>
  <sums>
    <sum>2+1</sum>
    <sum>3*2</sum>
  </sums>
  <divs>
    <div>3/2</div>
    <div>1/2</div>  
  </divs>
  <mults>
    <mult>3*5</mult>
    <mult>5*9</mult>
  </mults>
</example>

Or should I just use which I think is best? Are there some guidelines
or concerns with this? I couldn't find any info on this, or if it is
something I should worry when writing big xml files.

Thanks in advance for any information.

Best regards,
     Norberto.