doc: fix dead links to doc pages

doc/pages/highlighters.asciidoc

@@ -113,7 +113,7 @@ add-highlighter window/ regex //\h*(TODO:)[^\n]* 0:cyan 1:yellow,red
 
     capture_id can be either the capture number, or its name if a
     named capture is used in the regex (See
-    <<regex#Groups, `:doc regex Groups`>>)
+    <<regex#groups, `:doc regex groups`>>)
 
 *dynregex* <expression> <capture_id>:<face> ...::
     similar to regex, but expand (like a command parameter would) the

doc/pages/keys.asciidoc

@@ -817,7 +817,7 @@ The following keys are recognized by this mode to help with editing
 
 *<a-!>*::
     expand the typed expansions in currently entered text
-    (See <<expansions#typed-expansions,`:doc expansions typed-expansions`>>)
+    (See <<expansions#,`:doc expansions`>>)
 
 *<a-;>*, *<a-semicolon>*::
     escape to normal mode for a single command

doc/pages/modes.asciidoc

@@ -85,7 +85,7 @@ See prompt commands <<keys#prompt-commands,`:doc keys prompt-commands`>>.
 Mode entered with `<a-i>`, `<a-a>` and various combinations of `[]{}` keys.
 It aims at crafting semantic selections, often called *text-objects*.
 
-See object commands <<keys#object-commands,`:doc keys object-commands`>>.
+See object commands <<keys#object-selection,`:doc keys object-selection`>>.
 
 === User mode