Hi,
What I founded for mtexts:
"{\\fArial|b1|i0|c0|p34;your text}" => your text (bold)
"{\\fArial|b0|i1|c0|p34;your text}" => your text (italic)
"{\\fArial|b1|i1|c0|p34;your text}" => your text (bold and italic)
I'don't know about c and p options
Some others options available
"{\\Oyour} text" => overlines "your"
"{\\C1;your} text" => your text (color 1)
"{\\H5;your text}" => absolute height
"{\\H2x;your text}" => relative height
"{\\T2;your text}" => space between characters (from 0.75 to 4)
"{\\Q20;your text}" => inclination angle
"{\\W2;your text}" => relative width (stretch the text)