# modifier > Every PAG keyword record, with what grounds it and how it is checked. Page: Ontology · Grammar Canonical: https://banes-lab.com/ontology/grammar#pag-keywords-modifier Listed in [Ontology · Grammar](https://banes-lab.com/api/pages/ontology/grammar.md), after [declaration](https://banes-lab.com/ontology/grammar/pag-keywords-declaration.md) and before [coordination](https://banes-lab.com/ontology/grammar/pag-keywords-coordination.md). Every PAG keyword record, with what grounds it and how it is checked. ### MUST Details Meaning Mandatory requirement · a modifier inside a property Example MUST validate first Grounds [substrate-node:constraint](https://banes-lab.com/records/reasoning/substrate-node-constraint.md) How it is checked Checked by a structured-document validator that parses each document against the grammar and reports every defect by its shape Population Every agent and template document the validator walks, and every occurrence of the keyword in them Freshness A verdict stands until the grammar data or a document that uses the keyword changes Refusal The validation stage fails the gate on any defect code, so a document with a malformed keyword does not ship Observation None, because a keyword is static text in a document, and nothing observes it while a run executes Evidence Watched to fire and to accept: a suite plants a retired head in a real template and validates every agent and template on disk clean Authoritative side The grammar data, which every keyword in a document conforms to Depends on Not answered Shape it refuses Not answered ### NEVER Details Meaning Prohibition · a modifier inside a property Example NEVER delete without backup Grounds [substrate-node:constraint](https://banes-lab.com/records/reasoning/substrate-node-constraint.md) How it is checked Checked by a structured-document validator that parses each document against the grammar and reports every defect by its shape Population Every agent and template document the validator walks, and every occurrence of the keyword in them Freshness A verdict stands until the grammar data or a document that uses the keyword changes Refusal The validation stage fails the gate on any defect code, so a document with a malformed keyword does not ship Observation None, because a keyword is static text in a document, and nothing observes it while a run executes Evidence Watched to fire and to accept: a suite plants a retired head in a real template and validates every agent and template on disk clean Authoritative side The grammar data, which every keyword in a document conforms to Depends on Not answered Shape it refuses Not answered ### ALWAYS Details Meaning Invariance · a modifier inside a property Example ALWAYS log changes Grounds [substrate-node:constraint](https://banes-lab.com/records/reasoning/substrate-node-constraint.md) How it is checked Checked by a structured-document validator that parses each document against the grammar and reports every defect by its shape Population Every agent and template document the validator walks, and every occurrence of the keyword in them Freshness A verdict stands until the grammar data or a document that uses the keyword changes Refusal The validation stage fails the gate on any defect code, so a document with a malformed keyword does not ship Observation None, because a keyword is static text in a document, and nothing observes it while a run executes Evidence Watched to fire and to accept: a suite plants a retired head in a real template and validates every agent and template on disk clean Authoritative side The grammar data, which every keyword in a document conforms to Depends on Not answered Shape it refuses Not answered ### REQUIRED Details Meaning Necessity marker Example REQUIRED field Grounds [substrate-node:constraint](https://banes-lab.com/records/reasoning/substrate-node-constraint.md) How it is checked Checked by a structured-document validator that parses each document against the grammar and reports every defect by its shape Population Every agent and template document the validator walks, and every occurrence of the keyword in them Freshness A verdict stands until the grammar data or a document that uses the keyword changes Refusal The validation stage fails the gate on any defect code, so a document with a malformed keyword does not ship Observation None, because a keyword is static text in a document, and nothing observes it while a run executes Evidence Watched to fire and to accept: a suite plants a retired head in a real template and validates every agent and template on disk clean Authoritative side The grammar data, which every keyword in a document conforms to Depends on Not answered Shape it refuses Not answered ### MANDATORY Details Meaning Obligation marker Example MANDATORY check Grounds [substrate-node:constraint](https://banes-lab.com/records/reasoning/substrate-node-constraint.md) How it is checked Checked by a structured-document validator that parses each document against the grammar and reports every defect by its shape Population Every agent and template document the validator walks, and every occurrence of the keyword in them Freshness A verdict stands until the grammar data or a document that uses the keyword changes Refusal The validation stage fails the gate on any defect code, so a document with a malformed keyword does not ship Observation None, because a keyword is static text in a document, and nothing observes it while a run executes Evidence Watched to fire and to accept: a suite plants a retired head in a real template and validates every agent and template on disk clean Authoritative side The grammar data, which every keyword in a document conforms to Depends on Not answered Shape it refuses Not answered ### CRITICAL Details Meaning Repair ordering among failures, never a softer verdict Example CRITICAL validation Grounds [substrate-node:constraint](https://banes-lab.com/records/reasoning/substrate-node-constraint.md) How it is checked Checked by a structured-document validator that parses each document against the grammar and reports every defect by its shape Population Every agent and template document the validator walks, and every occurrence of the keyword in them Freshness A verdict stands until the grammar data or a document that uses the keyword changes Refusal The validation stage fails the gate on any defect code, so a document with a malformed keyword does not ship Observation None, because a keyword is static text in a document, and nothing observes it while a run executes Evidence Watched to fire and to accept: a suite plants a retired head in a real template and validates every agent and template on disk clean Authoritative side The grammar data, which every keyword in a document conforms to Depends on Not answered Shape it refuses Not answered ### ABSOLUTE Details Meaning No exceptions Example ABSOLUTE rule Grounds [substrate-node:constraint](https://banes-lab.com/records/reasoning/substrate-node-constraint.md) How it is checked Checked by a structured-document validator that parses each document against the grammar and reports every defect by its shape Population Every agent and template document the validator walks, and every occurrence of the keyword in them Freshness A verdict stands until the grammar data or a document that uses the keyword changes Refusal The validation stage fails the gate on any defect code, so a document with a malformed keyword does not ship Observation None, because a keyword is static text in a document, and nothing observes it while a run executes Evidence Watched to fire and to accept: a suite plants a retired head in a real template and validates every agent and template on disk clean Authoritative side The grammar data, which every keyword in a document conforms to Depends on Not answered Shape it refuses Not answered ### FORBIDDEN Details Meaning Absolute prohibition Example FORBIDDEN: direct DB Grounds [substrate-node:constraint](https://banes-lab.com/records/reasoning/substrate-node-constraint.md) How it is checked Checked by a structured-document validator that parses each document against the grammar and reports every defect by its shape Population Every agent and template document the validator walks, and every occurrence of the keyword in them Freshness A verdict stands until the grammar data or a document that uses the keyword changes Refusal The validation stage fails the gate on any defect code, so a document with a malformed keyword does not ship Observation None, because a keyword is static text in a document, and nothing observes it while a run executes Evidence Watched to fire and to accept: a suite plants a retired head in a real template and validates every agent and template on disk clean Authoritative side The grammar data, which every keyword in a document conforms to Depends on Not answered Shape it refuses Not answered ## Links to - [Constraint](https://banes-lab.com/records/reasoning/substrate-node-constraint.md)