Graphviz DOT is an actively used text markup language created in 2007.

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Example code from the web:

 // The graph name and the semicolons are optional
graph graphname {
    a -- b -- c;
    b -- d;
}

Example code from Linguist:

/* 
  Huffman Tree DOT graph.

  DOT Reference :  http://www.graphviz.org/doc/info/lang.html
                   http://en.wikipedia.org/wiki/DOT_language
  Timestamp     :  1415989074 
  Phrase        :  'OH GOD WHY IS LINGUIST SO ANAL ABOUT THIS STUFF'

  Generated on http://huffman.ooz.ie/
*/

digraph G {
    edge [label=0];
    graph [ranksep=0];
    T [shape=record, label="{{T|4}|000}"];
    S [shape=record, label="{{S|5}|001}"];
    SPACE [shape=record, label="{{SPACE|9}|01}"];
    A [shape=record, label="{{A|3}|1000}"];
    H [shape=record, label="{{H|3}|1001}"];
    U [shape=record, label="{{U|3}|1010}"];
    L [shape=record, label="{{L|2}|10110}"];
    N [shape=record, label="{{N|2}|10111}"];
    I [shape=record, label="{{I|4}|1100}"];
    O [shape=record, label="{{O|4}|1101}"];
    G [shape=record, label="{{G|2}|11100}"];
    F [shape=record, label="{{F|2}|11101}"];
    GF [label=4];
    W [shape=record, label="{{W|1}|111100}"];
    Y [shape=record, label="{{Y|1}|111101}"];
    B [shape=record, label="{{B|1}|111110}"];
    D [shape=record, label="{{D|1}|111111}"];
    BD [label=2];
    WYBD [label=4];
    GFWYBD [label=8];
    47 -> 18 -> 9 -> T;
    29 -> 13 -> 6 -> A;
    7 -> U;
    4 -> L;
    16 -> 8 -> I;
    GFWYBD -> GF -> G;
    WYBD -> 2 -> W;
    BD -> B;9 -> S [label=1];
    18 -> SPACE [label=1];
    6 -> H [label=1];
    13 -> 7 -> 4 -> N [label=1];
    8 -> O [label=1];
    GF -> F [label=1];
    2 -> Y [label=1];
    47 -> 29 -> 16 -> GFWYBD -> WYBD -> BD -> D [label=1];
}

Example code from Wikipedia:

digraph g {
	node [shape=plaintext];
	A1 -> B1;
	A2 -> B2;
	A3 -> B3;
	
	A1 -> A2 [label=f];
	A2 -> A3 [label=g];
	B2 -> B3 [label="g'"];
	B1 -> B3 [label="(g o f)'" tailport=s headport=s];

	{ rank=same; A1 A2 A3 }
	{ rank=same; B1 B2 B3 } 
}
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Last updated February 11th, 2019