ODF spreadsheet formulae have, according to the standard, "a namespace prefix
specifying the syntax and semantics used within the formula". Microsoft have
chosen to indicate their syntax and semantics with the msoxl: namespace, in
which for example text cells are (in some circumstances) treated as numbers for
the purposes of cell arithmetic.

OOo should support the possibility of alternative namespaces, initially with
msoxl: support in addition to the native OOo namespace. The option to bulk move
formulae into the msoxl: namespace in order to be able to save a document that
Excel users can open might also be of value, but the user should be warned that
Excel might evaluate formulae differently to OOo (although this will happen to
them unannounced if they open an OOo document in Google Docs, for instance).

Other ODF implementations also differ from OOo in their treatment of text values
in numeric formulae, and these differences could be resolved if namespaces could
be agreed that indicate this difference in behaviour. It may be that they choose
to adopt Microsoft's msoxl: as their default namespace anyway since they are
more in line with Excel's behaviour than with OOo's.

Functionality could be included to assist users in migrating formulae from
msoxl: or other namespaces to the native OOo namespace, performing speculative
evaluation in both in the original semantics and the native OOo namespace
semantics and identifying cells whose results differ.