Test 1: Invalid <mfrac> tag:

$\frac{}{}\frac{1}{2}$

Test 2: Invalid <mroot> tag:

$\text{exception 25:}\text{exception 25:}$

Test 3: Invalid <munder> tag:

$\underset{}{}\underset{2}{1}$

Test 4: Invalid <mover> tag:

$\stackrel{}{}\stackrel{2}{1}$

Test 5: Invalid <munderover> tag:

$\underset{}{\overset{}{}}\underset{2}{\overset{}{1}}\underset{2}{\overset{3}{1}}$

Test 6: Invalid <msub> tag:

${}_{}{1}_2$

Test 7: Invalid <msup> tag:

${}^{}{1}^2$

Test 8: Invalid <msubsup> tag:

${}_{}^{}{1}_2^{}{1}_2^3$

Test 9: Invalid <mmultiscripts> tag:

${}_{4}1_2^3{}_3{}^{4}1_2$