Specifically, in relation to field initializers (in this case, static) - §17.11 in ECMA 334:
If a class contains any static fields with initializers,
I know this question is very old, but here is the correct part of the specification:
ECMA-334 (C# Language Specification), Variable initializers, section 17.4.5:
When there are field declarations in multiple partial type declarations for the same type, the order of the parts is unspecified. However, within each part the field initializers are executed in order.
So the "textual order" in partial types is not undefined, rather it's partially defined. ;-)