[PATCH 5/9] StringList.trim_left() support logical tab width

Support logical width for tab characters in the trim_left() function.
---
 docutils/docutils/statemachine.py | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/docutils/docutils/statemachine.py b/docutils/docutils/statemachine.py
index 167cb7744..4b482c57e 100644
--- a/docutils/docutils/statemachine.py
+++ b/docutils/docutils/statemachine.py
@@ -1324,13 +1324,16 @@ class StringList(ViewList):
 
     """A `ViewList` with string-specific methods."""
 
-    def trim_left(self, length, start=0, end=sys.maxsize):
+    def trim_left(self, length, start=0, end=sys.maxsize, tab_width=8):
         """
-        Trim `length` characters off the beginning of each item, in-place,
-        from index `start` to `end`.  No whitespace-checking is done on the
-        trimmed text.  Does not affect slice parent.
+        Trim `length` logical characters off the beginning of each item,
+        in-place, from index `start` to `end`.  No whitespace-checking is done
+        on the trimmed text.  Does not affect slice parent.
+
+        A tab counts (depending on the column) for up to `tab_width` characters.
+        See `logical_rslice()` for details.
         """
-        self.data[start:end] = [line[length:]
+        self.data[start:end] = [logical_rslice(line, length, tab_width)
                                 for line in self.data[start:end]]
 
     def get_text_block(self, start, flush_left=False):