Each worksheet in a spreadsheet is represented by an XML document with a root element named <tt><worksheet></tt> in the [dead link]<tt>http://schemas.openxmlformats.org/spreadsheetml/2006/main</tt> Namespace.
The representation of date and time values in SpreadsheetML has attracted some criticism. ECMA-376 1st edition does not conform to ISO 8601:2004 "Representation of Dates and Times". It requires that implementations replicate a [[Lotus 1-2-3]] <ref>{{ cite web | url = http://www.exceluser.com/explore/earlydates.htm | title = How to Work With Dates Before 1900 in Excel | first = Charley | last = Kyd | date = October 2006 | work = ExcelUser | accessdate = 2009-09-16 }}</ref> bug that dictateserroneously thattreats 1900 isas a leap year, which in fact it isn't. Products complying with ECMA-376 would be required to use the WEEKDAY() spreadsheet function, and therefore assign incorrect dates to some days of the week, and also miscalculate the number of days between certain dates.<ref name="The Contradictory Nature of OOXML">{{ cite web | url=http://www.consortiuminfo.org/standardsblog/article.php?story=20070117145745854 | title=The Contradictory Nature of OOXML | publisher=ConsortiumInfo.org}}</ref> ECMA-376 2nd edition (ISO/IEC 29500) allows the use of 8601:2004 "Representation of Dates and Times" in addition to the Lotus 1-2-3 bug-compatible form.<ref>{{ cite web | url = http://www.ecma-international.org/publications/standards/Ecma-376.htm | title = ECMA-376 2nd edition Part 1 (3. Normative references) | publisher = Ecma-international.org | date = | accessdate = 2009-09-16}}</ref><ref>{{ cite web | url = http://www.ecma-international.org/news/TC45_current_work/New%20set%20of%20proposed%20dispositions%20posted.htm | title = New set of proposed dispositions posted, including more positive changes to the Ecma Office Open XML formats – Dispositions now proposed for more than half of National Bodies' comments | publisher = Ecma-international.org | date = 2007-12-11 | accessdate = 2009-09-16}}</ref>
