DOC: Document default cap styles

- remove '(default)' from cap style demo as this is only true for Line2D
  and the default rcParameters
- document default cap styles for Line2D and Patch in their cap style
  setters
- document default cap style for GraphicsContextBase in the same way as
  it's already done for joinstyle

Author: StefRe

lib/matplotlib/_enums.py

@@ -128,6 +128,9 @@ class CapStyle(str, _AutoStringNameEnum):
     For a visual impression of each *CapStyle*, `view these docs online
     <CapStyle>` or run `CapStyle.demo`.
 
+    By default, `~.backend_bases.GraphicsContextBase` draws a stroked line as
+    squared off at its endpoints.
+
     **Supported values:**
 
     .. rst-class:: value-list
@@ -168,7 +171,6 @@ def demo():
             ax.plot(xx, yy, lw=12, color='tab:blue', solid_capstyle=style)
             ax.plot(xx, yy, lw=1, color='black')
             ax.plot(xx, yy, 'o', color='tab:red', markersize=3)
-        ax.text(2.25, 0.55, '(default)', ha='center')
 
         ax.set_ylim(-.5, 1.5)
         ax.set_axis_off()

lib/matplotlib/lines.py

@@ -1336,6 +1336,8 @@ def set_dash_capstyle(self, s):
         """
         How to draw the end caps if the line is `~Line2D.is_dashed`.
 
+        The default capstyle is :rc:`lines.dash_capstyle`.
+
         Parameters
         ----------
         s : `.CapStyle` or %(CapStyle)s
@@ -1350,6 +1352,8 @@ def set_solid_capstyle(self, s):
         """
         How to draw the end caps if the line is solid (not `~Line2D.is_dashed`)
 
+        The default capstyle is :rc:`lines.solid_capstyle`.
+
         Parameters
         ----------
         s : `.CapStyle` or %(CapStyle)s

lib/matplotlib/patches.py

@@ -474,6 +474,9 @@ def set_capstyle(self, s):
         """
         Set the `.CapStyle`.
 
+        The default capstyle is 'round' for `.FancyArrowPatch` and 'butt' for
+        all other patches.
+
         Parameters
         ----------
         s : `.CapStyle` or %(CapStyle)s