206 Status Code Explained
A status code of 206 is a response to a request for part of a document. This is used by advanced caching tools, when a user agent requests only a small part of a page, and just that section is returned.
Why it Occurs
The HTTP 206 status code occurs if the response is the result of an If-Range request that used a strong cache validator. The response SHOULD NOT include other entity-headers. If the response is the result of an If-Range request that used a weak validator, the response MUST NOT include other entity-headers; this prevents inconsistencies between cached entity-bodies and updated headers.
What it Means
The response MUST include all of the entity-headers that would have been returned with a 200 (OK) response to the same request.A cache MUST NOT combine a 206 response with other previously cached content if the ETag or Last-Modified headers do not match exactly,A cache that does not support the Range and Content-Range headers MUST NOT cache 206 (Partial) responses.