In the 1970's programming languages:

became more structured (NOT to be confused with structured documents which are analogous to a later programming language paradigm.)

In programming languages, structured refers to the idea of nesting related pieces of program code.

Formatting languages:

also allowed nesting

But the major change in document preparation systems in the early to middle 70's were:

The first systems that allowed processing of non-textual elements such as mathematical formulas, tables, and drawings.

These are called integrated systems because they integrated text with non-textual elements.

Some of the early integrated processors are Tbl (1976), Eqn (1975) and tex (1979).

At about the same time:

The first WYSIWYG systems began to appear. These allow the writer to see an approximation on the screen of what will be printed on paper.

In programming languages:

Emphasis turned from operations (such as sorting) to data (the objects to be sorted)

And the object-oriented paradigm was born.

Smalltalk (1974) is considered the first truly object-oriented language

and CLU developed the idea of abstraction and information hiding which led to the object-oriented paradigm.

Document preparation systems followed suit in the 1980's ...

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