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    <title>attribute lspace rspace</title>
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    <!-- These operators are not from the operator dictionary, the default is spacing is lspace = rspace = thickmathspace = 5/18em. -->
    <math><mi>x</mi><mo lspace="0em" rspace="0em" style="margin-inline-start: 0.27777777777777em; margin-inline-end: 0.27777777777777em;">X</mo><mi>y</mi></math>
    <math><mi>x</mi><mo lspace="0em" rspace="0em" style="margin-inline-start: 1em; margin-inline-end: 0.27777777777777em;">X</mo><mi>y</mi></math>
    <math><mi>x</mi><mo lspace="0em" rspace="0em" style="margin-inline-start: 0.27777777777777em; margin-inline-end: 2em;">X</mo><mi>y</mi></math>
    <math><mi>x</mi><mo lspace="0em" rspace="0em" style="margin-inline-start: 3em; margin-inline-end: 4em;">X</mo><mi>y</mi></math>

    <br/>

    <!-- Same with multi-char <mo lspace="0em" rspace="0em">. -->
    <math><mi>x</mi><mo lspace="0em" rspace="0em" style="margin-inline-start: 0.27777777777777em; margin-inline-end: 0.27777777777777em;">XXX</mo><mi>y</mi></math>
    <math><mi>x</mi><mo lspace="0em" rspace="0em" style="margin-inline-start: 1em; margin-inline-end: 0.27777777777777em;">XXX</mo><mi>y</mi></math>
    <math><mi>x</mi><mo lspace="0em" rspace="0em" style="margin-inline-start: 0.27777777777777em; margin-inline-end: 2em;">XXX</mo><mi>y</mi></math>
    <math><mi>x</mi><mo lspace="0em" rspace="0em" style="margin-inline-start: 3em; margin-inline-end: 4em;">XXX</mo><mi>y</mi></math>

    <br/>

    <!-- This should have the default spacing from operator dictionary, that is rspace = rspace = mediummathspace = 4/18em. --> 
    <math><mi>x</mi><mo lspace="0em" rspace="0em" style="margin-inline-start: 0.22222222222222em; margin-inline-end: 0.22222222222222em;">+</mo><mi>y</mi></math>
    <math><mi>x</mi><mo lspace="0em" rspace="0em" style="margin-inline-start: 1em; margin-inline-end: 0.22222222222222em;">+</mo><mi>y</mi></math>
    <math><mi>x</mi><mo lspace="0em" rspace="0em" style="margin-inline-start: 0.22222222222222em; margin-inline-end: 2em;">+</mo><mi>y</mi></math>
    <math><mi>x</mi><mo lspace="0em" rspace="0em" style="margin-inline-start: 3em; margin-inline-end: 4em;">+</mo><mi>y</mi></math>

    <br/>

    <!-- Same with an explicit form="prefix". The default is now lspace=0 and rspace = veryverythinmathspace = 1/18em -->
    <math><mi>x</mi><mo lspace="0em" rspace="0em" style="margin-inline-start: 0em; margin-inline-end: 0.055555555555555em;">+</mo><mi>y</mi></math>
    <math><mi>x</mi><mo lspace="0em" rspace="0em" style="margin-inline-start: 1em; margin-inline-end: 0.055555555555555em;">+</mo><mi>y</mi></math>
    <math><mi>x</mi><mo lspace="0em" rspace="0em" style="margin-inline-start: 0em; margin-inline-end: 2em;">+</mo><mi>y</mi></math>
    <math><mi>x</mi><mo lspace="0em" rspace="0em" style="margin-inline-start: 3em; margin-inline-end: 4em;">+</mo><mi>y</mi></math>

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