`bold` (unary)
Bold
AsciiMath
bb(x)
LaTeX
\mathbf{x}
MathML
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
<mstyle displaystyle="true">
<mstyle mathvariant="bold">
<mi>x</mi>
</mstyle>
</mstyle>
</math>
OMML
<m:oMathPara>
<m:oMath>
<m:r>
<m:rPr>
<m:sty m:val="b"/>
</m:rPr>
<m:t>x</m:t>
</m:r>
</m:oMath>
</m:oMathPara>
UnicodeMath
\mbfd