Can I use <mspace> instead of "columnwidth" attribute in <mtable> elements?

For Web browsers that do not support the "columnwidth" attribute, you can add a blank row in the <mtable> element with <mspace width="*px"> to force the width of a given column.

You should also remove the whitespace after the blank row with rowspacing="0.0ex 1.0ex ..." attribute in the <mtable> element. For example:

Original equation:
    <math display="inline" displaystyle="normal">
    <mtable rowspacing="0.0ex" columnspacing="0.1in" columnalign="left">
      <mtr><mtd><mspace width="400px"></mspace></mtd><mtd></mtd></mtr>
      <mtr>
        <mtd><mi>y</mi><mo>=</mo><mfrac>
          <mrow> <msup><mi>x</mi><mn>2</mn></msup> <mo>&#x2212;</mo> <mn>4</mn> </mrow>
          <mrow> <mi>x</mi><mo>&#x2212;</mo><mn>2</mn> </mrow>
        </mfrac> </mtd>
        <mtd><mtext>(1)</mtext></mtd>
      </mtr>
    </mtable>
    </math>
Simplified version:
    <math display="inline" displaystyle="normal">
    <mtable rowspacing="0.0ex" columnspacing="0.1in" columnalign="left">
      <mtr><mtd><mspace height="0px" width="400px"></mspace></mtd><mtd></mtd></mtr>
      <mtr>
        <mtd><mi>y</mi><mo>=</mo><mi>x</mi><mo>+</mo><mn>2</mn></mtd>
        <mtd><mtext>(3)</mtext></mtd>
      </mtr>
    </mtable>
    </math>

The output in most browsers looks good:

Original equation:
    $\begin{array}{ll}& \\ y=\frac{x^2-4}{x-2}& \text{(1)}\end{array}$
Simplified version:
    $\begin{array}{ll}& \\ y=x+2& \text{(3)}\end{array}$

This is also a good workaround to replace the <mlabeledtr> element, which is deprecated now.

⇒ ISO 80000-2 Quantities and Units - Mathematics

⇐ Use "columnwidth" for Cross Formula Alignment

⇑ Alignment, Indentation and Line Breaks

⇑⇑ MathML (Mathematical Markup Language)