Tables
MathML tables are much alike to html tables in that they comprise of rows and columns. The main difference is that all items in a table data element must be enclosed within their respective element tags. for example:
<math><mtable><mtr><mtd><mi>x</mi><mo>+</mo><mi>y</mi></mtd></mtr><mtr><mtd><mi>y</mi><mo>+</mo><mi>x</mi></mtd></mtr></mtable></math>
gives:
Tables are used for matrices and other grid based number systems. They can be enclosed within brackets, aligned based on the other MathML elements etc.