? bb A
<math title="bb A">
  <mstyle mathcolor="red" displaystyle="true" fontfamily="serif">
    <mstyle fontweight="bold">
      <mi>A</mi>
    </mstyle>
  </mstyle>
</math>
$$\bf{A}$$

? bbb A
<math title="bbb A">
  <mstyle mathcolor="red" displaystyle="true" fontfamily="serif">
    <mstyle mathvariant="double-struck">&#xEF8C;</mstyle>
  </mstyle>
</math>
$$\mathds{A}$$

? cc A
<math title="cc A">
  <mstyle mathcolor="red" displaystyle="true" fontfamily="serif">
    <mstyle mathvariant="script">&#xEF35;</mstyle>
  </mstyle>
</math>
$$\cal{A}$$

? tt A
<math title="tt A">
  <mstyle mathcolor="red" displaystyle="true" fontfamily="serif">
    <mstyle fontfamily="monospace">
      <mi>A</mi>
    </mstyle>
  </mstyle>
</math>
$$\tt{A}$$

? fr A
<math title="fr A">
  <mstyle mathcolor="red" displaystyle="true" fontfamily="serif">
    <mstyle mathvariant="fraktur">&#xEF5D;</mstyle>
  </mstyle>
</math>
$$\mathfrak{A}$$

? sf A
<math title="sf A">
  <mstyle mathcolor="red" displaystyle="true" fontfamily="serif">
    <mstyle fontfamily="sans-serif">
      <mi>A</mi>
    </mstyle>
  </mstyle>
</math>
$$\sf{A}$$

? bb{AB3}.bbb(AB].cc(AB).fr{AB}.tt[AB].sf(AB)
<math title="bb{AB3}.bbb(AB].cc(AB).fr{AB}.tt[AB].sf(AB)">
  <mstyle mathcolor="red" displaystyle="true" fontfamily="serif">
    <mstyle fontweight="bold">
      <mrow>
        <mi>A</mi>
        <mi>B</mi>
        <mn>3</mn>
      </mrow>
    </mstyle>
    <mo>.</mo>
    <mstyle mathvariant="double-struck">
      <mrow>&#xEF8C;&#xEF8D;</mrow>
    </mstyle>
    <mo>.</mo>
    <mstyle mathvariant="script">
      <mrow>&#xEF35;&Bernoullis;</mrow>
    </mstyle>
    <mo>.</mo>
    <mstyle mathvariant="fraktur">
      <mrow>&#xEF5D;&#xEF5E;</mrow>
    </mstyle>
    <mo>.</mo>
    <mstyle fontfamily="monospace">
      <mrow>
        <mi>A</mi>
        <mi>B</mi>
      </mrow>
    </mstyle>
    <mo>.</mo>
    <mstyle fontfamily="sans-serif">
      <mrow>
        <mi>A</mi>
        <mi>B</mi>
      </mrow>
    </mstyle>
  </mstyle>
</math>
$$\bf{A B 3} . \mathds{A} \mathds{B} . \cal{A} \cal{B} . \mathfrak{A} \mathfrak{B} . \tt{A B} . \sf{A B}$$