Sgmltexi has a DTD where most of the elements are divided into two
categories, block and in-line, with the help of two parameter entities:
block and inline (SGML macro are
%block; and %inline;).
A block is something like a paragraph, a list, a table; an in-line is text, text emphatisation, anchors, cross references, and other things that stay inside a text.
Usually, but not necessarily, an in-line element contains text and possibly other in-line elements; but a block element may be made to contain in-line or other blocks. The Sgmltexi DTD don't consider the possibility of block elements that may contain either block or in-line. These kinds of contents are known as "flow" (this name is used inside the HTML DTD) and are rarely useful.
Some block elements, like example, may contain block
elements or a single pre element (a special block element
not classified as part of the %block; macro). The
pre element can contain only in-line that is preformatted,
that is: it maintains line breaks.
The two basic block element are shown in the following table:
| Element | Attribute | Content | Description or Texinfo equivalence
|
| p | in-line | paragraph, or simple block of text
| |
| indent | on, off
| first line indentation; default is on
| |
| center | in-line | @center
|