This video if the ESEF provides a particularly good explanation of the relationship between XHTML, XBRL, and Inline XBRL.
XBRL is an XML language. XML is really a family of languages/technologies which includes in part: XML Names, XML Base, XPath, XPointer, XLink, XML Schema, XSLT, XHTML (which is an application of XML).
XML is an ISO standard: ISO 8879:1986 "Information processing -- Text and office systems -- Standard Generalized Markup Language (SGML)".
XHTML, an application of XML, is likewise conformant to ISO 8879:1986.
Since XML is conformant to ISO 8879:1986 and XHTML is conformant to ISO 8879:1986; it seems to me that it can be said that both raw XBRL and Inline XBRL are conformant to ISO 8879:1986.