Fix BraceLabel.change_label() and document BraceText (#4347)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Francisco Manríquez Novoa <[email protected]>

Author: 3 people

manim/mobject/svg/brace.py

@@ -273,8 +273,10 @@ def shift_brace(self, obj: Mobject, **kwargs: Any) -> Self:
         return self
 
     def change_label(self, *text: str, **kwargs: Any) -> Self:
+        self.remove(self.label)
         self.label = self.label_constructor(*text, **kwargs)  # type: ignore[arg-type]
         self.brace.put_at_tip(self.label)
+        self.add(self.label)
         return self
 
     def change_brace_label(self, obj: Mobject, *text: str, **kwargs: Any) -> Self:
@@ -284,6 +286,50 @@ def change_brace_label(self, obj: Mobject, *text: str, **kwargs: Any) -> Self:
 
 
 class BraceText(BraceLabel):
+    """Create a brace with a text label attached.
+
+    Parameters
+    ----------
+    obj
+        The mobject adjacent to which the brace is placed.
+    text
+        The label text.
+    brace_direction
+        The direction of the brace. By default ``DOWN``.
+    label_constructor
+        A class or function used to construct a mobject representing
+        the label. By default :class:`~.Text`.
+    font_size
+        The font size of the label, passed to the ``label_constructor``.
+    buff
+        The buffer between the mobject and the brace.
+    brace_config
+        Arguments to be passed to :class:`.Brace`.
+    kwargs
+        Additional arguments to be passed to :class:`~.VMobject`.
+
+
+    Examples
+    --------
+        .. manim:: BraceTextExample
+            :save_last_frame:
+
+            class BraceTextExample(Scene):
+                def construct(self):
+                    s1 = Square().move_to(2*LEFT)
+                    self.add(s1)
+                    br1 = BraceText(s1, "Label")
+                    self.add(br1)
+
+                    s2 = Square().move_to(2*RIGHT)
+                    self.add(s2)
+                    br2 = BraceText(s2, "Label")
+
+                    br2.change_label("new")
+                    self.add(br2)
+                    self.wait(0.1)
+    """
+
     def __init__(
         self,
         obj: Mobject,