--- a/src/change.c
+++ b/src/change.c
@@ -988,7 +988,7 @@ ins_bytes_len(char_u *p, int len)
 
 /*
  * Insert or replace a single character at the cursor position.
- * When in REPLACE or VREPLACE mode, replace any existing character.
+ * When in MODE_REPLACE or MODE_VREPLACE state, replace any existing character.
  * Caller must have prepared for undo.
  * For multi-byte characters we get the whole character, the caller must
  * convert bytes to a character.
@@ -1119,7 +1119,7 @@ ins_char_bytes(char_u *buf, int charlen)
 
     // If we're in Insert or Replace mode and 'showmatch' is set, then briefly
     // show the match for right parens and braces.
-    if (p_sm && (State & INSERT)
+    if (p_sm && (State & MODE_INSERT)
 	    && msg_silent == 0
 	    && !ins_compl_active())
     {
@@ -1342,10 +1342,10 @@ del_bytes(
 /*
  * open_line: Add a new line below or above the current line.
  *
- * For VREPLACE mode, we only add a new line when we get to the end of the
- * file, otherwise we just start replacing the next line.
+ * For MODE_VREPLACE state, we only add a new line when we get to the end of
+ * the file, otherwise we just start replacing the next line.
  *
- * Caller must take care of undo.  Since VREPLACE may affect any number of
+ * Caller must take care of undo.  Since MODE_VREPLACE may affect any number of
  * lines however, it may call u_save_cursor() again when starting to change a
  * new line.
  * "flags": OPENLINE_DELSPACES	delete spaces after cursor
@@ -1416,7 +1416,7 @@ open_line(
 
     if (State & VREPLACE_FLAG)
     {
-	// With VREPLACE we make a copy of the next line, which we will be
+	// With MODE_VREPLACE we make a copy of the next line, which we will be
 	// starting to replace.  First make the new line empty and let vim play
 	// with the indenting and comment leader to its heart's content.  Then
 	// we grab what it ended up putting on the new line, put back the
@@ -1430,11 +1430,11 @@ open_line(
 	if (next_line == NULL)	    // out of memory!
 	    goto theend;
 
-	// In VREPLACE mode, a NL replaces the rest of the line, and starts
-	// replacing the next line, so push all of the characters left on the
-	// line onto the replace stack.  We'll push any other characters that
-	// might be replaced at the start of the next line (due to autoindent
-	// etc) a bit later.
+	// In MODE_VREPLACE state, a NL replaces the rest of the line, and
+	// starts replacing the next line, so push all of the characters left
+	// on the line onto the replace stack.  We'll push any other characters
+	// that might be replaced at the start of the next line (due to
+	// autoindent etc) a bit later.
 	replace_push(NUL);  // Call twice because BS over NL expects it
 	replace_push(NUL);
 	p = saved_line + curwin->w_cursor.col;
@@ -1448,7 +1448,7 @@ open_line(
 	saved_line[curwin->w_cursor.col] = NUL;
     }
 
-    if ((State & INSERT) && !(State & VREPLACE_FLAG))
+    if ((State & MODE_INSERT) && (State & VREPLACE_FLAG) == 0)
     {
 	p_extra = saved_line + curwin->w_cursor.col;
 #ifdef FEAT_SMARTINDENT
@@ -2077,7 +2077,7 @@ open_line(
 	}
     }
 
-    // (State == INSERT || State == REPLACE), only when dir == FORWARD
+    // (State == MODE_INSERT || State == MODE_REPLACE), only when dir == FORWARD
     if (p_extra != NULL)
     {
 	*p_extra = saved_char;		// restore char that NUL replaced
@@ -2085,8 +2085,9 @@ open_line(
 	// When 'ai' set or "flags" has OPENLINE_DELSPACES, skip to the first
 	// non-blank.
 	//
-	// When in REPLACE mode, put the deleted blanks on the replace stack,
-	// preceded by a NUL, so they can be put back when a BS is entered.
+	// When in MODE_REPLACE state, put the deleted blanks on the replace
+	// stack, preceded by a NUL, so they can be put back when a BS is
+	// entered.
 	if (REPLACE_NORMAL(State))
 	    replace_push(NUL);	    // end of extra blanks
 	if (curbuf->b_p_ai || (flags & OPENLINE_DELSPACES))
@@ -2156,7 +2157,7 @@ open_line(
 	    mark_adjust(curwin->w_cursor.lnum + 1, (linenr_T)MAXLNUM, 1L, 0L);
 	did_append = TRUE;
 #ifdef FEAT_PROP_POPUP
-	if ((State & INSERT) && !(State & VREPLACE_FLAG))
+	if ((State & MODE_INSERT) && (State & VREPLACE_FLAG) == 0)
 	    // properties after the split move to the next line
 	    adjust_props_for_split(curwin->w_cursor.lnum, curwin->w_cursor.lnum,
 						  curwin->w_cursor.col + 1, 0);
@@ -2164,7 +2165,7 @@ open_line(
     }
     else
     {
-	// In VREPLACE mode we are starting to replace the next line.
+	// In MODE_VREPLACE state we are starting to replace the next line.
 	curwin->w_cursor.lnum++;
 	if (curwin->w_cursor.lnum >= Insstart.lnum + vr_lines_changed)
 	{
@@ -2212,8 +2213,8 @@ open_line(
 
 	ai_col = curwin->w_cursor.col;
 
-	// In REPLACE mode, for each character in the new indent, there must
-	// be a NUL on the replace stack, for when it is deleted with BS
+	// In MODE_REPLACE state, for each character in the new indent, there
+	// must be a NUL on the replace stack, for when it is deleted with BS
 	if (REPLACE_NORMAL(State))
 	    for (n = 0; n < (int)curwin->w_cursor.col; ++n)
 		replace_push(NUL);
@@ -2224,8 +2225,8 @@ open_line(
 #endif
     }
 
-    // In REPLACE mode, for each character in the extra leader, there must be
-    // a NUL on the replace stack, for when it is deleted with BS.
+    // In MODE_REPLACE state, for each character in the extra leader, there
+    // must be a NUL on the replace stack, for when it is deleted with BS.
     if (REPLACE_NORMAL(State))
 	while (lead_len-- > 0)
 	    replace_push(NUL);
@@ -2234,7 +2235,7 @@ open_line(
 
     if (dir == FORWARD)
     {
-	if (trunc_line || (State & INSERT))
+	if (trunc_line || (State & MODE_INSERT))
 	{
 	    // truncate current line at cursor
 	    saved_line[curwin->w_cursor.col] = NUL;
@@ -2270,13 +2271,13 @@ open_line(
     curwin->w_cursor.coladd = 0;
 
 #if defined(FEAT_LISP) || defined(FEAT_CINDENT)
-    // In VREPLACE mode, we are handling the replace stack ourselves, so stop
-    // fixthisline() from doing it (via change_indent()) by telling it we're in
-    // normal INSERT mode.
+    // In MODE_VREPLACE state, we are handling the replace stack ourselves, so
+    // stop fixthisline() from doing it (via change_indent()) by telling it
+    // we're in normal MODE_INSERT state.
     if (State & VREPLACE_FLAG)
     {
 	vreplace_mode = State;	// So we know to put things right later
-	State = INSERT;
+	State = MODE_INSERT;
     }
     else
 	vreplace_mode = 0;
@@ -2305,9 +2306,9 @@ open_line(
 	State = vreplace_mode;
 #endif
 
-    // Finally, VREPLACE gets the stuff on the new line, then puts back the
-    // original line, and inserts the new stuff char by char, pushing old stuff
-    // onto the replace stack (via ins_char()).
+    // Finally, MODE_VREPLACE gets the stuff on the new line, then puts back
+    // the original line, and inserts the new stuff char by char, pushing old
+    // stuff onto the replace stack (via ins_char()).
     if (State & VREPLACE_FLAG)
     {
 	// Put new line in p_extra