Viewer: Allow modifying the current selection using Ctrl+Shift+arrow. Fixes #1855942 [[Enhancements] Comments and select text with keyboard](https://bugs.launchpad.net/calibre/+bug/1855942)

src/pyj/read_book/iframe.pyj

@@ -106,11 +106,16 @@ class IframeBoss:
             'get_current_cfi': self.get_current_cfi,
             'set_forward_keypresses': self.set_forward_keypresses,
             'set_reference_mode': self.set_reference_mode,
+            'modify_selection': self.modify_selection,
         }
         self.comm = IframeClient(handlers)
         self.last_window_ypos = 0
         self.length_before = None
 
+    def modify_selection(self, data):
+        sel = window.getSelection()
+        sel.modify('extend', data.direction, data.granularity)
+
     def set_forward_keypresses(self, data):
         self.forward_keypresses = data.forward
 

src/pyj/read_book/shortcuts.pyj

@@ -246,6 +246,18 @@ def shortcuts_definition():
         _('Search for next occurrence of selected text'),
     ),
 
+    'extend_selection_by_word': desc(
+        v"['Ctrl+Shift+ArrowRight']",
+        'ui',
+        _('Alter the current selection forward by a word'),
+    ),
+
+    'shrink_selection_by_word': desc(
+        v"['Ctrl+Shift+ArrowLeft']",
+        'ui',
+        _('Alter the current selection backwards by a word'),
+    ),
+
     'show_chrome': desc(
         v"['Escape', 'ContextMenu']",
         'ui',

src/pyj/read_book/view.pyj

@@ -405,7 +405,10 @@ class View:
             self.overlay.show_metadata()
         elif data.name is 'goto_location':
             self.overlay.show_ask_for_location()
-
+        elif data.name is 'shrink_selection_by_word':
+            self.iframe_wrapper.send_message('modify_selection', direction='backward', granularity='word')
+        elif data.name is 'extend_selection_by_word':
+            self.iframe_wrapper.send_message('modify_selection', direction='forward', granularity='word')
 
     def on_selection_change(self, data):
         self.currently_showing.selected_text = data.text