Non-standard: This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.
Feature-Policy: sync-xhr <allowlist>;
A list of origins for which the feature is allowed. See
By default the policy is set to
*, which means synchronous requests are allowed in all frames.
BCD tables only load in the browser