<semantics>

The <semantics> MathML element associates annotations with a MathML expression, for example its text source as a lightweight markup language or mathematical meaning expressed in a special XML dialect. Typically, its structure is

  • a first child which is a MathML expression to be annotated.
  • subsequent <annotation> or <annotation-xml> elements, the latter being reserved for XML formats such as OpenMath.

By default, only the first child of the <semantics> element is rendered while the others have their display set to none.

注意: 传统的 MathML 规范允许渲染器根据可用的注释决定默认渲染方式。以下确定可见子节点的规则已在某些浏览器中实现。有关 Presentation 和 Content MathML 之间的区别，请参阅 MathML 4。

  • 如果没有任何其他规则适用：默认情况下，仅渲染第一个子节点，该子节点应该是 Presentation MathML。
  • 如果第一个子节点是 Presentation MathML 元素（<annotation> 或 <annotation-xml> 除外），则渲染第一个子节点。
  • 如果没有找到 Presentation MathML，则渲染 <semantics> 的第一个 <annotation> 或 <annotation-xml> 子节点元素，这些元素没有 src 属性。对于 <annotation-xml> 元素，encoding 属性必须等于以下值之一
    • "application/mathml-presentation+xml"
    • "MathML-Presentation"
    • "SVG1.1"
    • "text/html"
    • "image/svg+xml"
    • "application/xml".

请注意，这里没有提到 "application/mathml+xml"，因为它不区分 Content 或 Presentation MathML。

属性

<semantics>、<annotation> 和 <annotation-xml> 元素接受 全局 MathML 属性。此外，可以在 <annotation> 和 <annotation-xml> 元素上设置以下属性

encoding

注释中语义信息的编码（例如 "MathML-Content"、"MathML-Presentation"、"application/openmath+xml"、"image/png"）

src

语义信息外部来源的位置。

示例

html
<math display="block">
  <semantics>
    <!-- The first child is the MathML expression rendered by default. -->
    <mrow>
      <msup>
        <mi>x</mi>
        <mn>2</mn>
      </msup>
      <mo>+</mo>
      <mi>y</mi>
    </mrow>

    <!-- Annotate with "Content MathML", a dedicated XML dialect to
         express the meaning of mathematical formulas. -->
    <annotation-xml encoding="MathML-Content">
      <apply>
        <plus />
        <apply>
          <power />
          <ci>x</ci>
          <cn type="integer">2</cn>
        </apply>
        <ci>y</ci>
      </apply>
    </annotation-xml>

    <!-- Annotate with a PNG image of the formula. -->
    <annotation encoding="image/png" src="some/path/formula.png" />

    <!-- Annotate with LaTeX, a lightweight markup language to write
         mathematical formulas. -->
    <annotation encoding="application/x-tex"> x^{2} + y </annotation>
  </semantics>
</math>

规范

规范
MathML Core
# semantics-and-presentation

浏览器兼容性

BCD 表仅在浏览器中加载