matplotlib · tfpf · 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
@@ -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()
diff --git a/lib/matplotlib/_mathtext.py b/lib/matplotlib/_mathtext.py
@@ -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()
@@ -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",
@@ -1843,6 +1845,7 @@ def csnames(group, names):
             | p.underset
             | p.sqrt
             | p.overline
+            | p.underline
         )
 
         p.simple        <<= (
@@ -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):

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
@@ -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"