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1 <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
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2 <!--
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3 This is a generated document. Do not edit.
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4 -->
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5 <HTML VERSION="2.0">
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6 <HEAD>
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7 <TITLE>The DOT Language</TITLE>
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8 </HEAD>
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9 <BODY BGCOLOR=white>
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10 <A NAME="top"></A>
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11 <H1 ALIGN=CENTER>The DOT Language</H1>
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12 <HR>
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13 The following is an abstract grammar defining the DOT language.
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14 Terminals are shown in bold font and nonterminals in italics.
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15 Literal characters are given in single quotes.
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16 Parentheses ( and ) indicate grouping when needed.
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17 Square brackets [ and ] enclose optional items.
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18 Vertical bars | separate alternatives.
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19 <TABLE>
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20 <TR>
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21 <TD ALIGN=RIGHT><I>graph</I></TD>
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22 <TD ALIGN=LEFT>:</TD>
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23 <TD ALIGN=LEFT>[ <B>strict</B> ] (<B>graph</B> | <B>digraph</B>) [ <I>ID</I> ] <B>'{'</B> <I>stmt_list</I> <B>'}'</B></TD>
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24 </TR>
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25 <TR>
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26 <TD ALIGN=RIGHT><I>stmt_list</I></TD>
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27 <TD ALIGN=LEFT>:</TD>
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28 <TD ALIGN=LEFT>[ <I>stmt</I> [ <B>';'</B> ] [ <I>stmt_list</I> ] ]</TD>
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29 </TR>
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30 <TR>
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31 <TD ALIGN=RIGHT><I>stmt</I></TD>
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32 <TD ALIGN=LEFT>:</TD>
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33 <TD ALIGN=LEFT><I>node_stmt</I></TD>
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34 </TR>
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35 <TR>
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36 <TD ALIGN=RIGHT></TD>
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37 <TD ALIGN=LEFT>|</TD>
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38 <TD ALIGN=LEFT><I>edge_stmt</I></TD>
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39 </TR>
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40 <TR>
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41 <TD ALIGN=RIGHT></TD>
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42 <TD ALIGN=LEFT>|</TD>
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43 <TD ALIGN=LEFT><I>attr_stmt</I></TD>
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44 </TR>
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45 <TR>
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46 <TD ALIGN=RIGHT></TD>
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47 <TD ALIGN=LEFT>|</TD>
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48 <TD ALIGN=LEFT><I>ID</I> <B>'='</B> <I>ID</I></TD>
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49 </TR>
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50 <TR>
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51 <TD ALIGN=RIGHT></TD>
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52 <TD ALIGN=LEFT>|</TD>
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53 <TD ALIGN=LEFT><I>subgraph</I></TD>
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54 </TR>
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55 <TR>
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56 <TD ALIGN=RIGHT><I>attr_stmt</I></TD>
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57 <TD ALIGN=LEFT>:</TD>
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58 <TD ALIGN=LEFT>(<B>graph</B> | <B>node</B> | <B>edge</B>) <I>attr_list</I></TD>
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59 </TR>
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60 <TR>
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61 <TD ALIGN=RIGHT><I>attr_list</I></TD>
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62 <TD ALIGN=LEFT>:</TD>
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63 <TD ALIGN=LEFT><B>'['</B> [ <I>a_list</I> ] <B>']'</B> [ <I>attr_list</I> ]</TD>
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64 </TR>
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65 <TR>
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66 <TD ALIGN=RIGHT><I>a_list</I></TD>
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67 <TD ALIGN=LEFT>:</TD>
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68 <TD ALIGN=LEFT><I>ID</I> [ <B>'='</B> <I>ID</I> ] [ <B>','</B> ] [ <I>a_list</I> ]</TD>
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69 </TR>
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70 <TR>
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71 <TD ALIGN=RIGHT><I>edge_stmt</I></TD>
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72 <TD ALIGN=LEFT>:</TD>
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73 <TD ALIGN=LEFT>(<I>node_id</I> | <I>subgraph</I>) <I>edgeRHS</I> [ <I>attr_list</I> ]</TD>
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74 </TR>
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75 <TR>
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76 <TD ALIGN=RIGHT><I>edgeRHS</I></TD>
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77 <TD ALIGN=LEFT>:</TD>
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78 <TD ALIGN=LEFT><I>edgeop</I> (<I>node_id</I> | <I>subgraph</I>) [ <I>edgeRHS</I> ]</TD>
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79 </TR>
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80 <TR>
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81 <TD ALIGN=RIGHT><I>node_stmt</I></TD>
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82 <TD ALIGN=LEFT>:</TD>
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83 <TD ALIGN=LEFT><I>node_id</I> [ <I>attr_list</I> ]</TD>
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84 </TR>
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85 <TR>
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86 <TD ALIGN=RIGHT><I>node_id</I></TD>
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87 <TD ALIGN=LEFT>:</TD>
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88 <TD ALIGN=LEFT><I>ID</I> [ <I>port</I> ]</TD>
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89 </TR>
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90 <TR>
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91 <TD ALIGN=RIGHT><I>port</I></TD>
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92 <TD ALIGN=LEFT>:</TD>
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93 <TD ALIGN=LEFT><B>':'</B> <I>ID</I> [ <B>':'</B> <I>compass_pt</I> ]</TD>
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94 </TR>
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95 <TR>
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96 <TD ALIGN=RIGHT></TD>
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97 <TD ALIGN=LEFT>|</TD>
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98 <TD ALIGN=LEFT><B>':'</B> <I>compass_pt</I></TD>
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99 </TR>
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100 <TR>
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101 <TD ALIGN=RIGHT><I>subgraph</I></TD>
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102 <TD ALIGN=LEFT>:</TD>
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103 <TD ALIGN=LEFT>[ <B>subgraph</B> [ <I>ID</I> ] ] <B>'{'</B> <I>stmt_list</I> <B>'}'</B></TD>
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104 </TR>
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105 <TR>
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106 <TD ALIGN=RIGHT><I>compass_pt</I></TD>
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107 <TD ALIGN=LEFT>:</TD>
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108 <TD ALIGN=LEFT>(<B>n</B> | <B>ne</B> | <B>e</B> | <B>se</B> | <B>s</B> | <B>sw</B> | <B>w</B> | <B>nw</B> | <B>c</B> | <B>_</B>)</TD>
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109 </TR>
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110 </TABLE>
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111 <P>
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112 The keywords <B>node</B>, <B>edge</B>, <B>graph</B>, <B>digraph</B>,
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113 <B>subgraph</B>, and <B>strict</B> are case-independent.
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114 Note also that the allowed compass point values are not keywords, so
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115 these strings can be used elsewhere as ordinary identifiers and, conversely,
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116 the parser will actually accept any identifier.
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117 <P>
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118 An <I>ID</I> is one of the following:
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119 <MENU>
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120 <LI> Any string of alphabetic (<TT>[a-zA-Z\200-\377]</TT>) characters, underscores (<TT>'_'</TT>) or
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121 digits (<TT>[0-9]</TT>), not beginning with a digit;
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122 <LI> a number [<tt>-</tt>]<sup>?</sup>(<tt>.</tt>[<tt>0</tt>-<tt>9</tt>]<sup>+</sup> | [<tt>0</tt>-<tt>9</tt>]<sup>+</sup>(<tt>.</tt>[<tt>0</tt>-<tt>9</tt>]<sup>*</sup>)<sup>?</sup> );
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123 <LI> any double-quoted string ("...") possibly containing escaped
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124 quotes (\")<SUP>1</SUP>;
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125 <LI> an <A NAME=html>HTML string</A> (<...>).
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126 </MENU>
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127 Note that in HTML strings, angle
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128 brackets must occur in matched pairs, and unescaped newlines are allowed.
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129 In addition, the content must be legal XML, so that the special XML
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130 escape sequences for ", &, <, and > may be necessary
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131 in order to embed these characters in attribute values or raw text.
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132 <P>
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133 Both quoted strings and HTML strings are scanned as a unit, so
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134 any embedded comments will be treated as part of the strings.
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135 <P>
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136 An <I>edgeop</I> is <TT>-></TT> in directed graphs and <TT>--</TT> in
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137 undirected graphs.
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138 <P>
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139 An <I>a_list</I> clause of the form <I>ID</I> is equivalent to
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140 <I>ID</I><TT>=true</TT>.
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141 <P>
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142 The language supports C++-style comments: <TT>/* */</TT> and <TT>//</TT>.
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143 In addition, a line beginning with a '#' character is considered a line
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144 output from a C preprocessor (e.g., # 34 to indicate line 34 ) and discarded.
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145 <P>
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146 Semicolons aid readability but are not required except in the rare case
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147 that a named subgraph with no body immediately preceeds an anonymous
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148 subgraph, since the precedence rules cause this sequence to be parsed as
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149 a subgraph with a heading and a body.
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150 Also, any amount of whitespace may be inserted between terminals.
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151 <P>
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152 As another aid for readability, dot allows single logical lines to
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153 span multiple physical lines using the standard C convention of a
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154 backslash immediately preceding a newline character. In addition,
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155 double-quoted strings can be concatenated using a '+' operator.
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156 As HTML strings can contain newline characters, they do not support the
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157 concatenation operator.
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158 <H2>Semantic Notes</H2>
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159 If a default attribute is
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160 defined using a <B>node</B>, <B>edge</B>, or <B>graph</B> statement,
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161 or by an attribute assignment not attached to a node or edge, any object of the
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162 appropriate type defined afterwards will inherit this attribute value.
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163 This holds until the default attribute is set to a new value, from which
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164 point the new value is used. Objects defined before a default attribute
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165 is set will have an empty string value attached to the attribute once
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166 the default attribute definition is made.
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167 <P>
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168 Note, in particular, that a subgraph receives the attribute settings of
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169 its parent graph at the time of its definition. This can be useful; for
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170 example, one can assign a font to the root graph and all subgraphs will
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171 also use the font. For some attributes, however, this property is
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172 undesirable. If one attaches a label to the root graph, it is probably
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173 not the desired effect to have the label used by all subgraphs. Rather
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174 than listing the graph attribute at the top of the graph, and the
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175 resetting the attribute as needed in the subgraphs, one can simple defer
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176 the attribute definition if the graph until the appropriate subgraphs
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177 have been defined.
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178 <P>
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179 If an edge belongs to a cluster, its endpoints belong to that cluster.
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180 Thus, where you put an edge can effect a layout, as clusters are sometimes
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181 laid out recursively.
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182 <H2>Character encodings</H2>
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183 The DOT language assumes at least the ascii character set.
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184 Quoted strings, both ordinary and HTML-like, may contain non-ascii characters.
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185 In most cases, these strings are uninterpreted: they simply serve as
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186 unique identifiers or values passed through untouched. Labels, however,
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187 are meant to be displayed, which requires that the software be able to
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188 compute the size of the text and determine the appropriate glyphs.
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189 For this, it needs to know what character encoding is used.
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190 <P>
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191 By default, DOT assumes the UTF-8 character encoding. It also accepts
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192 the Latin1 (ISO-8859-1) character set, assuming the input graph uses
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193 the <B><A HREF=attrs.html#a:charset>charset</A></B> attribute to
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194 specify this. For graphs using other
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195 character sets, there are usually programs, such as <TT>iconv</TT>, which
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196 will translate from one character set to another.
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197 <P>
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198 Another way to avoid non-ascii characters in labels is to use HTML entities
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199 for special characters. During label evaluation, these entities are
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200 translated into the underlying character. This
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201 <a HREF="http://www.graphviz.org/doc/char.html">
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202 table</a> shows the supported entities, with their Unicode value, a typical
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203 glyph, and the HTML entity name. Thus, to include a lower-case Greek beta
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204 into a string, one can use the ascii sequence <TT>&beta;</TT>.
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205 In general, one should only use entities that are allowed in the output
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206 character set, and for which there is a glyph in the font.
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207 <HR>
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208 <OL TYPE="1">
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209 <LI> In quoted strings in DOT, the only escaped character is double-quote
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210 ("). That is, in quoted strings, the dyad \" is converted to "; all other
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211 characters are left unchanged. In particular, \\ remains \\. Layout
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212 engines may apply additional escape sequences.
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213 </OL>
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214 </BODY>
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215 </HTML>
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