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| <a name="Introduction"></a> | |
| <a name="SEC1"></a> | |
| <h1 class="chapter"> <a href="libtextstyle_toc.html#TOC1">1. Introduction</a> </h1> | |
| <p>Text is easier to read when it is accompanied with styling information, | |
| such as color, font attributes (weight, posture), or underlining, and | |
| this styling is customized appropriately for the output device. | |
| </p> | |
| <p>GNU libtextstyle provides an easy way to add styling to programs that | |
| produce output to a console or terminal emulator window. It does this | |
| in a way that allows the end user to customize the styling using the | |
| industry standard, namely Cascading Style Sheets (CSS). | |
| </p> | |
| <a name="Style-definitions"></a> | |
| <a name="SEC2"></a> | |
| <h2 class="section"> <a href="libtextstyle_toc.html#TOC2">1.1 Style definitions</a> </h2> | |
| <p>Let's look at the traditional way styling is done for specific programs. | |
| </p> | |
| <p>Browsers, when they render HTML, use CSS styling. | |
| </p> | |
| <p>The older approach to user-customizable text styling is that the user | |
| associates patterns with escape sequences in an environment variable or a | |
| command-line argument. This is the approach used, for example, by the | |
| GNU ‘<samp>ls</samp>’ program in combination with the ‘<samp>dircolors</samp>’ program. | |
| The processing is distributed across several steps: | |
| </p><ol> | |
| <li> | |
| There is default style definition that is hard-coded in the | |
| ‘<samp>dircolors</samp>’ program. The user can also define their own definitions | |
| in a file such as ‘<tt>~/.dir_colors</tt>’. This style definition contains | |
| explicit terminal escape sequences; thus, it can only be used with | |
| consoles and terminal emulators, and each style definition applies only | |
| to a certain class of mostly-compatible terminal emulators. | |
| </li><li> | |
| The <code>dircolors</code> program, when invoked, translates such a style | |
| definition to a sequence of shell statements that sets an environment | |
| variable <code>LS_COLORS</code>. | |
| </li><li> | |
| The shell executes these statements, and thus sets the environment | |
| variable <code>LS_COLORS</code>. | |
| </li><li> | |
| The program looks at the environment variable and emits the listed escape | |
| sequences. | |
| </li></ol> | |
| <p>In contrast, this library implements styling as follows: | |
| </p><ol> | |
| <li> | |
| There is a default style definition in a CSS file that is part of the | |
| same package as the stylable program. The user can also define their own | |
| definitions in a CSS file, and set an environment environment variable to | |
| point to it. | |
| </li><li> | |
| The program looks at the environment variable, parses the CSS file, | |
| translates the styling specifications to the form that is appropriate for | |
| the output device (escape sequences for terminal emulators, inline CSS | |
| and <code><span></code> elements for HTML output), and emits it. | |
| </li></ol> | |
| <p>Thus, with GNU libtextstyle, the styling has the following properties: | |
| </p><ul> | |
| <li> | |
| It is easier for the user to define their own styling, because the file | |
| format is standardized and supported by numerous syntax aware editors. | |
| </li><li> | |
| A styling file does not depend on the particular output device. An HTML | |
| output and a black-on-white terminal emulator can use the same styling | |
| file. A white-on-black (or even green-on-black) terminal emulator will | |
| need different styling, though. | |
| </li><li> | |
| It is simpler: There is no need for a program that converts the style | |
| specification from one format to another. | |
| </li></ul> | |
| <a name="Built_002din-versus-separate-styling"></a> | |
| <a name="SEC3"></a> | |
| <h2 class="section"> <a href="libtextstyle_toc.html#TOC3">1.2 Built-in versus separate styling</a> </h2> | |
| <p>There are generally two approaches for adding styling to text: | |
| </p><ul> | |
| <li> | |
| The program that generates the text adds the styling. It does so through | |
| interleaved statements that turn on or off specific attributes. | |
| </li><li> | |
| The styling gets added by a separate program, that postprocesses the | |
| output. This separate program usually uses regular expressions to | |
| determine which text regions to style with a certain set of text | |
| attributes. | |
| </li></ul> | |
| <p>The first approach produces a styling that is 100% correct, regardless of | |
| the complexity of the text that is being output. This is the preferred | |
| approach for example for JSON, XML, or programming language text. | |
| </p> | |
| <p>The second approach works well if the output has a simple, easy-to-parse | |
| format. It may produce wrong styling in some cases when the text format | |
| is more complex. This approach is often used for viewing log files. | |
| </p> | |
| <p>GNU libtextstyle supports both approaches; it includes an example program | |
| for each of the two approaches. | |
| </p> | |
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| <tr><td valign="middle" align="left">[<a href="#SEC1" title="Beginning of this chapter or previous chapter"> << </a>]</td> | |
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| <td valign="middle" align="left">[<a href="libtextstyle_toc.html#SEC_Top" title="Cover (top) of document">Top</a>]</td> | |
| <td valign="middle" align="left">[<a href="libtextstyle_toc.html#SEC_Contents" title="Table of contents">Contents</a>]</td> | |
| <td valign="middle" align="left">[<a href="libtextstyle_5.html#SEC45" title="Index">Index</a>]</td> | |
| <td valign="middle" align="left">[<a href="libtextstyle_abt.html#SEC_About" title="About (help)"> ? </a>]</td> | |
| </tr></table> | |
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