[Yaml-core] Controlling Emmision

[Brian I. <in...@tt...>]

Steve Howell and I (he lives 3 doors down from me) figured out a way to
control the specific formatting of a particular YAML document. (ie map sort
order, etc) Simply define parallel YAML structures that give hints to the
emitter on how to structure output.

For instance, I am considering adding an option to YAML.pm that would allow
you to specify a document like this:

---
- orderDate
- shipTo: &A [name, street, city, state, zip, country]
- billTo: *A
- comment
- items:
    '*': [partNum, productName, quantity, USPrice, comment, shipDate]

So that a document like this would always have the same key orders:

--- #YAML:1.0 !ingerson.com/purchaseOrder/^document
orderDate: 1999-10-20
shipTo: !^Address
    name: Alice Smith
    street: '123 Maple Street'
    city: Mill Valley
    state: CA
    zip: 90210
    country: US
billTo: !^Address
    name: Robert Smith
    street: '8 Oak Avenue'
    city: Old Town
    state: PA
    zip: 95819
    country: US
comment: Hurry, my lawn is going wild!
items: 
    - !^item
        partNum: '872-AA'
        productName: Lawnmower
        quantity: 1
        USPrice: 148.95
        comment: Confirm this is electric
    - !^item  
        partNum: '926-AA'
        productName: Baby Monitor
        quantity: 1
        USPrice: 39.98
        shipDate: 1999-05-21

This is basically a stopgap measure until we have incremental emission and/or
a formalized schema language for defining such issues.

Cheers, Brian