2.1.688 Part 4 Section 220.127.116.11, v (Cell Value)
a. The standard does not limit the length of the value of this element.
Excel restricts the value of this element to be at most 32767 characters.
b. The standard does not place content restrictions on values based on the t attribute.
Office places the following value restrictions based on the cell type:
If the cell contains a string, the value shall be a zero-based index into the shared string table, pointing to the actual string value.
If the cell contains a number, the value shall be a textual representation of a double-precision floating point number.
If the cell contains a Boolean, the value shall be 1 to specify true and 0 to specify false.
If the cell contains an error, the value shall be one of the following text strings: #NULL!, #DIV/0!, #VALUE!, #REF!, #NAME?, #NUM!, or #N/A.
Cells containing formulas express the last calculated result of the formula in this element.
A spreadsheet application may use inline strings to bypass creating the shared string table. Inline strings are specified by the is element under the c element instead of the v element under the c element. Inline strings are specified in the same way a string would be expressed in the shared string table. See the is element ("[ECMA-376] Part 4 §18.104.22.168; is") for an example.
c. The standard makes no mention of an xml:space attribute.
Excel uses this attribute to specify, using the W3C space preservation rules, how white space should be handled for the element's contents; its allowed values are defined by the XML 1.0 specification.