What does the "s" attribute signify in a cell tag in XLSX

The s attribute refers to a style. "237" is a style defined in the styles.xml file.

<v>39448</v>

...is most likely a date in double format. And the style 237 tells excel to display 39448 in date format.

You can see an example of how this works here: http://blogs.msdn.com/b/brian_jones/archive/2007/05/29/simple-spreadsheetml-file-part-3-formatting.aspx

The s attribute refers that is equal to 237, point to the 237th element found in parent element in the styles.xml file contained in the xlsx file.

If the cell value is a date, the element can be similar to the following code

<xf numFmtId="167"     fontId="6"     fillId="0"     borderId="6"     xfId="3"     applyNumberFormat="1"     applyFont="1"     applyFill="1"     applyBorder="1"     applyAlignment="1">        <alignment horizontal="center"/></xf>

At this point we don't see that this cell represent a date type.To understand that, we must find the <numFmtId> with "167" as key.

This value can be found at begin of styles.xml file

<numFmts count="7">    <numFmt numFmtId="164" formatCode="[$-409]d\-mmm\-yy;@"/>    <numFmt numFmtId="165" formatCode="0.000"/>    <numFmt numFmtId="166" formatCode="0.0"/>    <numFmt numFmtId="167" formatCode="[$-409]d\-mmm\-yyyy;@"/>    <numFmt numFmtId="168" formatCode="0.0%"/>    <numFmt numFmtId="169" formatCode="00000"/>    <numFmt numFmtId="170" formatCode="0.0000"/></numFmts>

The line with numFmtId="167" indicate that the cell's value is a date formatted using following string "[$-409]d-mmm-yyyy;@"

In resume, to find if a cell contains a number or date we must

1. find the S (=style) attribute of <c> element
2. find the numFmtId attribute of the <xf> element in styles.xml file in xlsx file.
3. find the formatCode attribute of <numFmt> that has numFmtId as key
4. see if format is a date format or a number format

I hope that can help others.