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kdl/SCHEMA-SPEC.md

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KDL Schema Specification

The KDL Schema specification describes a schema language for use with KDL, written in KDL itself. A schema language allows users to describe and constrain the allowed semantics of a KDL document. This can be used for many purposes: documentation for users, automated verification, or even automated generation of bindings!

Definition

document node

This is the toplevel node in a KDL Schema. It is required, and there must be exactly one, at the very toplevel of a document.

Values

None.

Properties

  • description (optional): An informational description of the purpose of this schema.
  • schema-url (optional): A URL where someone may go to find more information about this schema. It is not meant for mechanical processing.

Children

  • node - zero or more toplevel nodes for the KDL document this schema describes.

node node

The node node describes node instances in a document. These may either be at the toplevel of the document, or they may be nested inside a children block in another node.

Values

  • Node name (optional) - A string name for the node. If present, the node's rules/validations will apply only to children with this node name. Otherwise, the rules will apply to all child nodes, regardless of whether they're named or not.

Properties

  • description (optional): An informational description of the purpose of this node.
  • id (optional): A globally unique identifier for this node.
  • ref (optional): A globally unique reference to another node's ID. If present, all properties, values, and children defined in the target node will be copied to this node, replacing any conflicts.

Children

  • min (optional): Minimum number of this kind of node (or any node, if the name is missing) allowed in the parent's children block.
  • max (optional): Maximum number of this kind of node (or any node, if the name is missing) allowed in the parent's children block.
  • prop - zero or more properties for this node.
  • value - zero or more values for this node.
  • children - zero or more children for this node.

prop node

value node

children node

The Schema

For the full KDL Schema schema itself, see examples/kdl-schema.kdl.