Previously, the Cart API's bundled section rendering operated in the context of
/cart when no specific
sections_url parameter was set. Now, when
sections_url isn't set, sections are rendered in the context of the current page, based on the Referer HTTP request header.
The behavior when
sections_url is set remains unchanged.
For most themes, this change won't be disruptive. If the section being requested exists in the context of the current page, then using the Referer as the context for rendering, instead of
/cart, shouldn't present any issues.
For more information on bundled section rendering, refer to the Ajax API's Cart reference.