SGML

Languages ​​designed according to the rules of SGML are suitable for hand typing -- there is less marking than later in XML. However, the existence of a DTD and connection to it to describe the structure of each document were compulsory.

SGML later, in the late 90 years, became the basis for formulation of XML as a format easier for machine processing, not necessarily requiring to describe the structure of documents for each file.