Store tags in lower case.

README.md

@@ -220,7 +220,7 @@ Shell completion scripts for Bash, Fish and Zsh can be found in respective subdi
 - URLs are unique in DB. The same URL cannot be added twice.
 - Bookmarks with immutable titles are listed with bold `(L)` after the URL.
 - **Tags**:
-  - Comma (`,`) is the tag delimiter in DB. A tag cannot have comma(s) in it. Tags are filtered (for unique tags) and sorted. Tags can be replaced.
+  - Comma (`,`) is the tag delimiter in DB. A tag cannot have comma(s) in it. Tags are filtered (for unique tags) and sorted. Tags are stored in lower case and can be replaced, appended or deleted.
 - **Update** operation:
   - If --title, --tag or --comment is passed without argument, clear the corresponding field from DB.
   - If --url is passed (and --title is omitted), update the title from web using the URL.

buku.1

@@ -34,7 +34,7 @@ URLs are unique in DB. The same URL cannot be added twice.
 Bookmarks with immutable titles are listed with bold '(L)' after the URL.
 .PP
 \fITags\fR:
-  - Comma (',') is the tag delimiter in DB. A tag cannot have comma(s) in it. Tags are filtered (for unique tags) and sorted. Tags can be replaced.
+  - Comma (',') is the tag delimiter in DB. A tag cannot have comma(s) in it. Tags are filtered (for unique tags) and sorted. Tags are stored in lower case and can be replaced, appended or deleted.
 .PP
 \fIUpdate\fR operation:
   - If --title, --tag or --comment is passed without argument, clear the corresponding field from DB.

buku.py

@@ -1624,11 +1624,12 @@ def parse_tags(keywords=None):
 
     orig_tags += tags.strip(DELIM).split(DELIM)
     for tag in orig_tags:
-        if tag not in unique_tags:
-            unique_tags += (tag, )  # Select unique tags
+        if tag.lower() not in unique_tags:
+            # Add unique tags in lowercase
+            unique_tags += (tag.lower(), )
 
     # Sort the tags
-    sorted_tags = sorted(unique_tags, key=str.lower)
+    sorted_tags = sorted(unique_tags)
 
     # Wrap with delimiter
     return '%s%s%s' % (DELIM, DELIM.join(sorted_tags), DELIM)