extpfeil

The extpfeil extension adds more macros for producing extensible arrows, including \xtwoheadrightarrow, \xtwoheadleftarrow, \xmapsto, \xlongequal, \xtofrom, and a non-standard \Newextarrow for creating your own extensible arrows. The latter has the form

\Newextarrow{\cs}{lspace,rspace}{unicode-char}

where \cs is the new control sequence name to be defined, lspace and rspace are integers representing the amount of space (in suitably small units) to use at the left and right of text that is placed above or below the arrow, and unicode-char is a number representing a unicode character position in either decimal or hexadecimal notation.

For example

\Newextarrow{\xrightharpoonup}{5,10}{0x21C0}

defines an extensible right harpoon with barb up. Note that MathJax knows how to stretch only a limited number of characters, so you may not actually get a stretchy character this way. The characters that can be stretched may also depend on the font you have selected.

This extension is loaded automatically when the autoload extension is used. To load the extpfeil extension explicitly, add '[tex]/extpfeil' to the load array of the loader block of your MathJax configuration, and add 'extpfeil' to the packages array of the tex block.

window.MathJax = {
  loader: {load: ['[tex]/extpfeil']},
  tex: {packages: {'[+]': ['extpfeil']}}
};

Alternatively, use \require{extpfeil} in a TeX expression to load it dynamically from within the math on the page, if the require extension is loaded.

---