Data & schema semantics · Size & shape

x-ms-header-collection-prefix

`x-ms-header-collection-prefix` appears on header objects. Its value is a string. Used by a single provider across 3 OpenAPI documents. It sits in the `x-ms-` namespace, so its meaning is defined by ms tooling rather than by OpenAPI. Observed values include `x-ms-meta-`, `x-ms-or-`. Consistent with size & shape — this is inferred from where the key appears and what it carries, not from any published definition.

Data & schema semantics x-ms- namespace derived description

How this description was produced. It is assembled from what was measured in the corpus — where this key appears in a document, what shape its value takes, the values observed, and how many providers use it. It is not taken from a published definition, because for most extensions none exists. Read it as evidence, not as a specification. If you own this extension and want it described properly, tell us.

19 occurrences

3 documents

1 providers

vendor-named

Where it appears

Location in the document	Occurrences
header	15
parameter	4

What its value looks like

Value shape	Occurrences
string	19

Observed values

Sampled from the specifications, most frequent first.

x-ms-meta-x-ms-or-

Providers publishing it

All 1.

microsoft-azure

Why this is not in OpenAPI

Extensions exist because a provider needed something the specification would not carry. Most of what they hold is not the API contract at all — it is operational metadata about the contract: documentation, lifecycle, policy, provenance, and now agents. That metadata is usually better placed alongside the contract, in an Overlay or an APIs.json index, than crammed inside it. See everything else doing the data & schema semantics job.