Wrong use of `pattern` in examples

[danielfett]

Looking at the current editor's draft, it seems that the JSON schema pattern feature is used in a wrong way in most of the examples.

pattern always represents a regular expression, not a static string match. There's also no implicit anchoring.

That means that, for example, the definition

                        "id": {
                          "type": "string",
                          "pattern": "https://bank-standards.example.com#accounts"
                        }

matches the string https://bank-standards.example.com#accounts but also https://bank-standardsxexample.com#accounts (different domain) and https://bank-standards.example.com#accountsAndWhatNot (substring matching).

The definition

"pattern": "did:example:123|did:example:456"

matches the string xdid:example:123x.

A demo of these problems in JSON schema can be found here.

This is a potential security issue.

Regular expressions need to be anchored explitly (using $ and ^) and any special characters need to be escaped properly. const should be used where pattern is not required.

[andorsk]

Discussed on a DIF call:

@danielfett very reasonable concern. We discussed as a group and see two areas of improvement:

1. Fix the examples
2. Mention syntax related standard JSONSchema regex syntax: to https://json-schema.org/understanding-json-schema/reference/regular_expressions.html

To address by 2.1.