Aug 14, 2022 · Aug 15, 2022 · Aug 15, 2022
diff --git a/doc/users/next_whats_new/mathtext_underline.rst b/doc/users/next_whats_new/mathtext_underline.rst
 Underlining text while using Mathtext
 -------------------------------------

 Mathtext now supports the ``\underline`` command.

 .. code-block:: python

    import matplotlib.pyplot as plt
    plt.text(0.4, 0.7, r'This is $\underline{underlined}$ text.')
    plt.text(0.4, 0.3, r'So is $\underline{\mathrm{this}}$.')
    plt.show()
diff --git a/lib/matplotlib/_mathtext.py b/lib/matplotlib/_mathtext.py
        p.group            = Forward()
        p.operatorname     = Forward()
        p.overline         = Forward()
        p.underline        = Forward()
        p.overset          = Forward()
        p.placeable        = Forward()
        p.required_group   = Forward()
            + p.required_group("value"))

        p.overline <<= cmd(r"\overline", p.required_group("body"))
        p.underline <<= cmd(r"\underline", p.required_group("body"))

        p.overset  <<= cmd(
            r"\overset",
            | p.underset
            | p.sqrt
            | p.overline
            | p.underline
        )

        p.simple        <<= (
        hlist = Hlist([rightside])
        return [hlist]

    def underline(self, s, loc, toks):
        body = toks["body"]

        state = self.get_state()
        thickness = state.get_current_underline_thickness()

        # Place underline below body (loosely based on node735).
        kern = 3 * thickness
        vlist = Vlist([Hlist([body]), Kern(kern), Hrule(state, thickness)])
        vlist.shift_amount = kern + thickness / 2 + body.depth

        hlist = Hlist([vlist])
        return [hlist]

    def _auto_sized_delimiter(self, front, middle, back):
        state = self.get_state()
        if len(middle):
diff --git a/lib/matplotlib/tests/baseline_images/test_mathtext/mathtext1_dejavusans_04.png b/lib/matplotlib/tests/baseline_images/test_mathtext/mathtext1_dejavusans_04.png
diff --git a/lib/matplotlib/tests/test_mathtext.py b/lib/matplotlib/tests/test_mathtext.py
    r'$x \overset{f}{\rightarrow} \overset{f}{x} \underset{xx}{ff} \overset{xx}{ff} \underset{f}{x} \underset{f}{\leftarrow} x$',  # github issue #18241
    r'$\sum x\quad\sum^nx\quad\sum_nx\quad\sum_n^nx\quad\prod x\quad\prod^nx\quad\prod_nx\quad\prod_n^nx$',  # GitHub issue 18085
    r'$1.$ $2.$ $19680801.$ $a.$ $b.$ $mpl.$',
    r'Matplotlib: $\underline{Plotting}$ $\underline{\mathrm{with}}$ Python',  # GitHub issue 14235
 ]

 digits = "0123456789"
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,11 @@
		Underlining text while using Mathtext
		-------------------------------------

		Mathtext now supports the ``\underline`` command.

		.. code-block:: python

		import matplotlib.pyplot as plt
		plt.text(0.4, 0.7, r'This is $\underline{underlined}$ text.')
		plt.text(0.4, 0.3, r'So is $\underline{\mathrm{this}}$.')
		plt.show()
Original file line number	Diff line number	Diff line change
Expand Up		@@ -1770,6 +1770,7 @@ def csnames(group, names):
		p.group = Forward()
		p.operatorname = Forward()
		p.overline = Forward()
		p.underline = Forward()
		p.overset = Forward()
		p.placeable = Forward()
		p.required_group = Forward()
Expand DownExpand Up		@@ -1820,6 +1821,7 @@ def csnames(group, names):
		+ p.required_group("value"))

		p.overline <<= cmd(r"\overline", p.required_group("body"))
		p.underline <<= cmd(r"\underline", p.required_group("body"))

		p.overset <<= cmd(
		r"\overset",
Expand All		@@ -1843,6 +1845,7 @@ def csnames(group, names):
		\| p.underset
		\| p.sqrt
		\| p.overline
		\| p.underline
		)

		p.simple <<= (
Expand DownExpand Up		@@ -2478,6 +2481,20 @@ def overline(self, s, loc, toks):
		hlist = Hlist([rightside])
		return [hlist]

		def underline(self, s, loc, toks):
		body = toks["body"]

		state = self.get_state()
		thickness = state.get_current_underline_thickness()

		# Place underline below body (loosely based on node735).
		kern = 3 * thickness
		vlist = Vlist([Hlist([body]), Kern(kern), Hrule(state, thickness)])
		vlist.shift_amount = kern + thickness / 2 + body.depth

		hlist = Hlist([vlist])
		return [hlist]

		def _auto_sized_delimiter(self, front, middle, back):
		state = self.get_state()
		if len(middle):
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -129,6 +129,7 @@
		r'$x \overset{f}{\rightarrow} \overset{f}{x} \underset{xx}{ff} \overset{xx}{ff} \underset{f}{x} \underset{f}{\leftarrow} x$', # github issue #18241
		r'$\sum x\quad\sum^nx\quad\sum_nx\quad\sum_n^nx\quad\prod x\quad\prod^nx\quad\prod_nx\quad\prod_n^nx$', # GitHub issue 18085
		r'$1.$ $2.$ $19680801.$ $a.$ $b.$ $mpl.$',
		r'Matplotlib: $\underline{Plotting}$ $\underline{\mathrm{with}}$ Python', # GitHub issue 14235
		]

		digits = "0123456789"
Expand Down