refer to core regex section from patternProperties and pattern

Author: gregsdennis

specs/jsonschema-core.md

@@ -1686,9 +1686,8 @@ The presence of this keyword affects the behaviors of
 ##### `patternProperties`
 
 The value of `patternProperties` MUST be an object. Each property name of this
-object SHOULD be a valid regular expression, according to the ECMA-262 regular
-expression dialect. Each property value of this object MUST be a valid JSON
-Schema.
+object SHOULD be a valid regular expression as indicated in {{regex}}. Each
+property value of this object MUST be a valid JSON Schema.
 
 Validation succeeds if, for each instance name that matches any regular
 expressions that appear as a property name in this keyword's value, the child

specs/jsonschema-validation.md

@@ -210,7 +210,8 @@ Omitting this keyword has the same behavior as a value of 0.
 #### `pattern` {#pattern}
 
 The value of this keyword MUST be a string. This string SHOULD be a valid
-regular expression, according to the ECMA-262 regular expression dialect.
+regular expression as indicated in {{jsonschema-core#regex}}.
+<!-- need to verify the {{section}} syntax works across files somehow -->
 
 A string instance is considered valid if the regular expression matches the
 instance successfully. Recall: regular expressions are not implicitly anchored.