Why is tex designed to render spaces around brackets?

Question

When I wrote following lines:

\section{Introduction}{
  Content in introduction ...
}

Unwanted space comes before Content as warned.

I understand it's due to some technical decision in tex. But I wonder the reasons behind this decision.

At the beginning of text tags in HTML, literal spaces do not get rendered. I actually prefer behavior like this, because it makes my handcrafted code more readable.

By the way, can I have tex ignore spaces between { and Content of this code?

Answer 1

Commands that expect an argument can be defined to ignore white space (typically use of \ignorespaces and/or \unskip) (eg \footnotetext{ a} is the same as \footnotetext{a} the fact that spaces are not ignored around {} in running text is a general feature so \LaTeX{} is... is a common way of making the space appear.

HTML is different as it is a fixed tag set and special parsing rules are added for each element. XML does not drop white space for example. So the situation in TeX is similar to that in XHTML: The parser does not drop space but the definition of particular commands may be such that it ignores the space tokens.

Answer 2

Ignoring the spaces after \section{Introduction} is standard LaTeX behavior, with or without braces. Spaces do not appear in the output before "Content" in the following minimal example:

\documentclass{article}
\begin{document}
\section{Introduction}{
  Content in introduction ...
}
\end{document}

This uses the article document class, but most of the common classes behave the same.

So the problem occurs because of something else in your document. I suspect an odd definition of \section, either in your document or in your document class.

Answer 3

The \section command has one mandatory argument, the section title (and an optional argument, but this is irrelevant here).

The text of the section goes after the title and not inside braces:

 \section{Introduction}

 This is silly text, but shows how one should do.

 The introduction has more than one paragraph; paragraphs
 are separated by a blank line.

 Enough for the introduction.

 \section{Main results}

 Here we'll show the wonderful results we got.

 ...

LaTeX is not HTML and has no concept of tags similar to HTML ones, though some constructs (the environments) can remind of them.