Amendment 1 to the SGML standard changes the minimum literal at the start of the SGML Declaration (that is ISO 8879-1986 changed to ISO 8879:1986). This change has caused considerable confusion and difficulty. Some SGML supporting products require one, some the other, and others allow either.
To alleviate the trouble caused by strict adherence to the standard, OmniMark allows both forms of the minimum literal, but reports a warning (rather than an error) when it encounters the ISO 8879-1986 form. When warnings are suppressed in an OmniMark run, no indication of this error will be given.
It should be kept in mind, however, that anything other than ISO 8879:1986 is, strictly speaking, an error, even though for convenience OmniMark reports the older form only as a warning.