why git-completion.bash is not autocompleting show-ref?

The git autocompletion has show and show-branch but not show-ref. Is this because autocompletion list is not complete? or is there any other reason?

[note] I am using the la开发者_如何学编程test git from source (git version 1.7.5.128.g50d30)

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Come to think of it, that was the asnwer, of course:

I think show-ref is plumbing, not porcelain

Porcelain can be used in various contexts including non-standard (overriden GIT_DIR, GIT_WORK_TREE, temporary directories, locks, whatnot). It would be ill-advised to use completion scripts indiscriminately during such operations, because they would invariably rely on other git subcommands, that may not exactly be valid at that time

This is my theory, people are welcome to supplement that :)