Implement the default registry in the spec (#659)

* Implement the default registry in the spec

This PR copies the number and date/time default functionality from design to the specification.

The copy was done verbatim, except:

- I moved some parts of number to make the structure logically consistent
- I added an example to the `style=percent` note
- I turned the information about the default selector into an "important" note

* Apply suggestions from code review

Co-authored-by: Eemeli Aro <[email protected]>

* Update spec/registry.md

* Update spec/registry.md

Co-authored-by: Eemeli Aro <[email protected]>

* Update spec/registry.md

Co-authored-by: Eemeli Aro <[email protected]>

* Update spec/registry.md

Co-authored-by: Eemeli Aro <[email protected]>

* Fix heading levels

* Apply suggestions from code review

Co-authored-by: Richard Gibson <[email protected]>

* Address @gibson042 comments

* Add `:string`

Also clarifies that the "data model" in this section is for the registry, not the other data model deliverable.

* Apply suggestions from code review

Co-authored-by: Tim Chevalier <[email protected]>

* Emit invalid expression

@catamorphism is correct: what a function can emit for an unsupported operand is "invalid expression". Presumably a resolution error would occur _before_ the function is called. Other types of errors, such as selection error, happen afterwards.

* Update spec/registry.md

Co-authored-by: Tim Chevalier <[email protected]>

* Update spec/registry.md

Co-authored-by: Tim Chevalier <[email protected]>

* Apply suggestions from code review

Co-authored-by: Tim Chevalier <[email protected]>

* Fix note formatting

* Address comments about literals

* Mention/require (`SHOULD`) users to use NFC

* Update spec/registry.md

Co-authored-by: Eemeli Aro <[email protected]>

* Update spec/registry.md

Co-authored-by: Eemeli Aro <[email protected]>

* Update spec/registry.md

* Update spec/registry.md

Co-authored-by: Eemeli Aro <[email protected]>

* Update spec/registry.md

Co-authored-by: Eemeli Aro <[email protected]>

* Apply suggestions from code review

Co-authored-by: Eemeli Aro <[email protected]>

* Fix my mistake about _style options_

* Update spec/registry.md

Co-authored-by: Eemeli Aro <[email protected]>

* Update spec/registry.md

Co-authored-by: Eemeli Aro <[email protected]>

* Fix the Java example

---------

Co-authored-by: Eemeli Aro <[email protected]>
Co-authored-by: Richard Gibson <[email protected]>
Co-authored-by: Tim Chevalier <[email protected]>

Author: 4 people