- General outline
- Describe the node uniqueness constraint

- Define domain for uniqueness
- Define domain for existence

- Use hex integers for rgb examples

- Specify general constraint language
- Specify `UNIQUE` operator
- Clearly define semantics for domain and expressions
- List all concrete constraints in example section
- Add several more examples

They are more appropriate under the Semantics and Syntax sections, respectively.

Move Errors section

References opencypher#172

- Remove TODO
- Add example using larger pattern
- Add example using multiple `exists()`

- Rename `constrait-expr` to `constraint-predicate`
- Limit scope of `UNIQUE` to single properties only
- Update examples to reflect `PRIMARY KEY`

- Remove erroneous example for composing `NODE KEY` with `UNIQUE` and `exists()`
- Rephrase example section to describe `NODE KEY` more accurately.

- Add missing case for when an error should be raised

Add test for DROP

For improved source readability

- use same EBNF style as @hvub did in opencypher#493
- use links to connect to grammar constructs in openCypher grammar spec
- modify constraint operators to be suffix-modeled, ala IS NOT NULL
- introduce 'grouped-expression' concept

Extend definition to reference grouped expression

- Update definition to reference grouped expression
- Reformulate equivalence example to use IS NOT NULL and IS UNIQUE over a grouped expression

Move ahead of referencing sections to ease readability of CIP

- Including links to these from the CIP
- Also update examples for the parser tests