While interpreting a formula expression, string content is now converted
to numeric values if conversion is unambiguous, or a #VALUE! error is
set if no unambiguous conversion is possible.
Converted are only integer numbers including exponent, and ISO 8601
dates and times in their extended formats with separators. Anything
else, especially fractional values with decimal separators or dates
other than ISO 8601 would be locale dependent and are not converted.
Leading and trailing blanks are ignored.
The century CC may not be omitted and the two-digit year setting is not
taken into account. Instead of the T date and time separator exactly one
blank may be used.
If a date is given, it must be a valid Gregorian calendar date. In this
case the optional time must be in the range 00:00 to 23:59:59.99999...
If only time is given, it may have any value for hours, taking elapsed
time into account; minutes and seconds are limited to the value 59 as
The conversion is done for single arguments, either referenced cell
content or inline string, cell range arguments are not affected, so
SUM(A1:A2) now will differ from A1+A2 if at least one of the cells
contain a convertible string, as in Excel ...
Because the conversion is also done for formula inline strings, such as
="1999-11-22"+42, calculations involving inline localized dates now
return an error, e.g. with "11/22/1999" or "22.11.1999".
Conversion on the fly naturally is significantly slower than calculating
with numeric values. Plus, as said, various values are not automatically
converted as the conversion may be ambiguous.