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1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html401/loose.dtd">
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2 <html>
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3 <!-- Created on February, 21 2024 by texi2html 1.78a -->
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5 Written by: Lionel Cons <Lionel.Cons@cern.ch> (original author)
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6 Karl Berry <karl@freefriends.org>
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12 -->
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13 <head>
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14 <title>GNU libtextstyle: 1. Introduction</title>
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15
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16 <meta name="description" content="GNU libtextstyle: 1. Introduction">
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17 <meta name="keywords" content="GNU libtextstyle: 1. Introduction">
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18 <meta name="resource-type" content="document">
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22 <style type="text/css">
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35 ul.toc {list-style: none}
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36 -->
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37 </style>
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38
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39
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40 </head>
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41
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42 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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43
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44 <table cellpadding="1" cellspacing="1" border="0">
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45 <tr><td valign="middle" align="left">[ << ]</td>
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46 <td valign="middle" align="left">[<a href="libtextstyle_2.html#SEC4" title="Next chapter"> >> </a>]</td>
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47 <td valign="middle" align="left"> </td>
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48 <td valign="middle" align="left"> </td>
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49 <td valign="middle" align="left"> </td>
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50 <td valign="middle" align="left"> </td>
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51 <td valign="middle" align="left"> </td>
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52 <td valign="middle" align="left">[<a href="libtextstyle_toc.html#SEC_Top" title="Cover (top) of document">Top</a>]</td>
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53 <td valign="middle" align="left">[<a href="libtextstyle_toc.html#SEC_Contents" title="Table of contents">Contents</a>]</td>
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54 <td valign="middle" align="left">[<a href="libtextstyle_5.html#SEC46" title="Index">Index</a>]</td>
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55 <td valign="middle" align="left">[<a href="libtextstyle_abt.html#SEC_About" title="About (help)"> ? </a>]</td>
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56 </tr></table>
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57
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58 <hr size="2">
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59 <a name="Introduction"></a>
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60 <a name="SEC1"></a>
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61 <h1 class="chapter"> <a href="libtextstyle_toc.html#TOC1">1. Introduction</a> </h1>
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62
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63 <p>Text is easier to read when it is accompanied with styling information,
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64 such as color, font attributes (weight, posture), or underlining, and
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65 this styling is customized appropriately for the output device.
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66 </p>
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67 <p>GNU libtextstyle provides an easy way to add styling to programs that
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68 produce output to a console or terminal emulator window. It does this
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69 in a way that allows the end user to customize the styling using the
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70 industry standard, namely Cascading Style Sheets (CSS).
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71 </p>
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72
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73
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74 <a name="Style-definitions"></a>
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75 <a name="SEC2"></a>
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76 <h2 class="section"> <a href="libtextstyle_toc.html#TOC2">1.1 Style definitions</a> </h2>
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77
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78 <p>Let's look at the traditional way styling is done for specific programs.
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79 </p>
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80 <p>Browsers, when they render HTML, use CSS styling.
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81 </p>
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82 <p>The older approach to user-customizable text styling is that the user
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83 associates patterns with escape sequences in an environment variable or a
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84 command-line argument. This is the approach used, for example, by the
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85 GNU ‘<samp>ls</samp>’ program in combination with the ‘<samp>dircolors</samp>’ program.
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86 The processing is distributed across several steps:
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87 </p><ol>
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88 <li>
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89 There is default style definition that is hard-coded in the
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90 ‘<samp>dircolors</samp>’ program. The user can also define their own definitions
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91 in a file such as ‘<tt>~/.dir_colors</tt>’. This style definition contains
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92 explicit terminal escape sequences; thus, it can only be used with
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93 consoles and terminal emulators, and each style definition applies only
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94 to a certain class of mostly-compatible terminal emulators.
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95 </li><li>
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96 The <code>dircolors</code> program, when invoked, translates such a style
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97 definition to a sequence of shell statements that sets an environment
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98 variable <code>LS_COLORS</code>.
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99 </li><li>
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100 The shell executes these statements, and thus sets the environment
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101 variable <code>LS_COLORS</code>.
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102 </li><li>
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103 The program looks at the environment variable and emits the listed escape
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104 sequences.
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105 </li></ol>
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106
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107 <p>In contrast, this library implements styling as follows:
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108 </p><ol>
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109 <li>
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110 There is a default style definition in a CSS file that is part of the
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111 same package as the stylable program. The user can also define their own
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112 definitions in a CSS file, and set an environment environment variable to
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113 point to it.
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114 </li><li>
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115 The program looks at the environment variable, parses the CSS file,
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116 translates the styling specifications to the form that is appropriate for
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117 the output device (escape sequences for terminal emulators, inline CSS
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118 and <code><span></code> elements for HTML output), and emits it.
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119 </li></ol>
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120
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121 <p>Thus, with GNU libtextstyle, the styling has the following properties:
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122 </p><ul>
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123 <li>
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124 It is easier for the user to define their own styling, because the file
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125 format is standardized and supported by numerous syntax aware editors.
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126 </li><li>
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127 A styling file does not depend on the particular output device. An HTML
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128 output and a black-on-white terminal emulator can use the same styling
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129 file. A white-on-black (or even green-on-black) terminal emulator will
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130 need different styling, though.
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131 </li><li>
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132 It is simpler: There is no need for a program that converts the style
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133 specification from one format to another.
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134 </li></ul>
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135
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136
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137 <a name="Built_002din-versus-separate-styling"></a>
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138 <a name="SEC3"></a>
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139 <h2 class="section"> <a href="libtextstyle_toc.html#TOC3">1.2 Built-in versus separate styling</a> </h2>
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140
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141 <p>There are generally two approaches for adding styling to text:
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142 </p><ul>
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143 <li>
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144 The program that generates the text adds the styling. It does so through
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145 interleaved statements that turn on or off specific attributes.
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146 </li><li>
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147 The styling gets added by a separate program, that postprocesses the
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148 output. This separate program usually uses regular expressions to
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149 determine which text regions to style with a certain set of text
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150 attributes.
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151 </li></ul>
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152
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153 <p>The first approach produces a styling that is 100% correct, regardless of
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154 the complexity of the text that is being output. This is the preferred
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155 approach for example for JSON, XML, or programming language text.
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156 </p>
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157 <p>The second approach works well if the output has a simple, easy-to-parse
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158 format. It may produce wrong styling in some cases when the text format
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159 is more complex. This approach is often used for viewing log files.
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160 </p>
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161 <p>GNU libtextstyle supports both approaches; it includes an example program
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162 for each of the two approaches.
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163 </p>
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164
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165 <table cellpadding="1" cellspacing="1" border="0">
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166 <tr><td valign="middle" align="left">[<a href="#SEC1" title="Beginning of this chapter or previous chapter"> << </a>]</td>
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167 <td valign="middle" align="left">[<a href="libtextstyle_2.html#SEC4" title="Next chapter"> >> </a>]</td>
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168 <td valign="middle" align="left"> </td>
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169 <td valign="middle" align="left"> </td>
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170 <td valign="middle" align="left"> </td>
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171 <td valign="middle" align="left"> </td>
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172 <td valign="middle" align="left"> </td>
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173 <td valign="middle" align="left">[<a href="libtextstyle_toc.html#SEC_Top" title="Cover (top) of document">Top</a>]</td>
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174 <td valign="middle" align="left">[<a href="libtextstyle_toc.html#SEC_Contents" title="Table of contents">Contents</a>]</td>
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175 <td valign="middle" align="left">[<a href="libtextstyle_5.html#SEC46" title="Index">Index</a>]</td>
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176 <td valign="middle" align="left">[<a href="libtextstyle_abt.html#SEC_About" title="About (help)"> ? </a>]</td>
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177 </tr></table>
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178 <p>
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179 <font size="-1">
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180 This document was generated by <em>Bruno Haible</em> on <em>February, 21 2024</em> using <a href="https://www.nongnu.org/texi2html/"><em>texi2html 1.78a</em></a>.
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181 </font>
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182 <br>
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183
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184 </p>
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185 </body>
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186 </html>
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