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Block and in-line

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