rowspacing specifies how much space to add between rows. columnspacing specifies how much space to add between columns. MathJax uses these attributes to implement many LaTeX commands. Note that Firefox does not support these attributes yet. You may find some reftests here: http://devel.mathjax.org/testing/testsuite/MathMLToDisplay/Presentation/TablesAndMatrices/
Created attachment 171150 [details] Testcase for @columnalign
@columnalign is crucial for formatting multi-line equations (as in the testcase).