2.1.1113 Part 4 Section 3.18.36, ST_Formula (Formula)
a. The standard does not limit the length of the contents of the ST_Formula simple type.
Excel restricts the contents of this simple type to be at most 8192 characters.
b. The standard is missing reference to general formulas syntax and prose.
In Excel, the ST_Formula simple type should have a reference to general formulas syntax and prose as defined in Formulas ("[ECMA-376] Part 4 §3.17; Formulas").