Comments

A comment is a rich text note that is attached to & associated with a cell, separate from other cell content. Comment content is stored separate from the cell, and is displayed in a drawing object (like a text box) that is separate from, but associated with, a cell. Comments are used as reminders, such as noting how a complex formula works, or to provide feedback to other users. Comments can also be used to explain assumptions made in a formula or to call out something special about the cell.

example:

<comments>
  <authors>
    <author>Bob</author>
    <author>CBR</author>
  </authors>
  <commentList>
    <comment ref="D4" authorId="0">
      <text>
        <r>
          <rPr>
            <b/>
            <sz val="8"/>
            <color indexed="81"/>
            <rFont val="Calibri"/>
            <charset val="1"/>
            <scheme val="minor"/>
          </rPr>
          <t>Bob:</t>
        </r>
        <r>
          <rPr>
            <sz val="8"/>
           <color indexed="81"/>
           <rFont val="Calibri"/>
           <charset val="1"/>
           <scheme val="minor"/>
         </rPr>
         <t xml:space="preserve">Why such high expense?</t>
       </r>
     </text>
    </comment>
  </commentList>
</comments>

This xml sample displays a comment by "Bob" (bolded) that says, "Why such high expense?" (non bolded).