Import the patch of Eckehard Berns to add insert mode. Thanks!

st.c

@@ -2100,6 +2100,10 @@ tputc(char *c, int len) {
 		sel.bx = -1;
 	if(IS_SET(MODE_WRAP) && term.c.state & CURSOR_WRAPNEXT)
 		tnewline(1); /* always go to first col */
+	if(IS_SET(MODE_INSERT) && term.c.x+1 < term.col)
+		memmove(&term.line[term.c.y][term.c.x+1],
+			&term.line[term.c.y][term.c.x],
+			(term.col - term.c.x - 1) * sizeof(Glyph));
 	tsetchar(c, &term.c.attr, term.c.x, term.c.y);
 	if(term.c.x+1 < term.col)
 		tmoveto(term.c.x+1, term.c.y);

st.info

@@ -153,6 +153,7 @@ st| simpleterm,
 	ritm=\E[23m,
 	rmacs=\E(B,
 	rmcup=\E[?1049l,
+	rmir=\E[4l,
 	rmkx=\E[?1l\E>,
 	rmso=\E[23m,
 	rmul=\E[m,
@@ -168,6 +169,7 @@ st| simpleterm,
 	sitm=\E[3m,
 	smacs=\E(0,
 	smcup=\E[?1049h,
+	smir=\E[4h,
 	smkx=\E[?1h\E=,
 	smso=\E[3m,
 	smul=\E[4m,