lfs-book-zh_CN/appendixa/flex-desc.xml

<sect2>
<title>Contents</title>

<para>The Flex package contains the flex program</para>

</sect2>

<sect2><title>Description</title>

<para>Flex is a tool for generating programs which recognizes patterns in text. 
Pattern recognition is very useful in many applications. A user sets up rules 
what to look for and flex will make a program that looks for those
patterns. The reason people use flex is that it is much easier to set up 
rules for what to look for than to write the actual program that finds 
the text.</para>

</sect2>