proposal: testing: relax lower-case suffix requirement for example test annotation

[kortschak]

Background

The testing package provides a mechanism to produce distinct examples for a single package, function, type or method.

Multiple example functions for a package/type/function/method may be provided by appending a distinct suffix to the name. The suffix must start with a lower-case letter.

func Example_suffix() { ... }
func ExampleF_suffix() { ... }
func ExampleT_suffix() { ... }
func ExampleT_M_suffix() { ... }

Currently, this is specified to be defined by a suffix that starts with a lower-case letter. This restrictions is presumably to ensure that a method (which must start with an upper-case letter to be justified in having a documentation example by virtue of being exported) is distinguishable from a suffix tag. The godoc command has always allowed numeric and first characters, enabling the use of culturally conventional numbered examples and use of 'words' that start with a number (see #43454 for the motivation for this proposal). It's worth noting that the only requirement for distinguishing between a method _M and a human-directed _suffix would be that the suffix can not be interpretable as a method worth documenting; it must not have an upper-case initial.

Proposal

Relax the documented restriction to be "The suffix must not start with an upper-case letter."