indentation

English

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An indentation can mean two things:

• To make notches in something or form deep recesses in a coastline for instance.
• To place text farther to the right to separate it from surrounding text.

The first meaning is also applied in hardness measurement as in indentation hardness.

For an example of the second meaning, this is an indentation of one non-breaking space:

 Indented block

and this is an indentation of two non-breaking spaces:

  Indented block 2

In the written form of many languages, an indentation is often used at the beginning of a line to signal the start of a new paragraph.

Outdentation is a neologism used in computer circles to describe placing text back to the left again.

Some languages (e.g. Hebrew, Arabic) are written right-to-left, and if indentation is used, in the above "left" and "right" should of course be swapped when referring to such languages.

Indentation in typesetting

There are two main types of first-line indent: normal and hanging. A "normal" indent indents the first line, as shown here, an indent of one centimetre:

The other kind, a hanging indent, indents the rest of the text while leaving the first line in place; as shown here with a hanging indent of one centimetre:

Indentation in programming

In computer programming languages, indentation is used to format program source code in order to improve its readability. Indentation is generally only of use to programmers; compilers and interpreters rarely care how much whitespace is present in between programming statements. However, certain programming languages rely on the use of indentation in order to demarcate programming structure, often using a variation of the off-side rule. The Haskell, Occam, and Python programming languages rely on indentation in this way.

Debates over where to indent, whether to use spaces or tabs, and how many spaces to use are often hotly debated among programmers, leading some to classify indentation as a religious war^[1]. Different indentation styles are commonly used. In 2006 a third method of indentation was proposed, called elastic tabstops.

Notes and references