diff --git a/src/terminal.c b/src/terminal.c
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+/* vi:set ts=8 sts=4 sw=4 noet:
+ *
+ * VIM - Vi IMproved	by Bram Moolenaar
+ *
+ * Do ":help uganda"  in Vim to read copying and usage conditions.
+ * Do ":help credits" in Vim to see a list of people who contributed.
+ * See README.txt for an overview of the Vim source code.
+ */
+
+/*
+ * Terminal window support, see ":help :terminal".
+ *
+ * For a terminal one VTerm is constructed.  This uses libvterm.  A copy of
+ * that library is in the libvterm directory.
+ *
+ * The VTerm invokes callbacks when its screen contents changes.  The line
+ * range is stored in tl_dirty_row_start and tl_dirty_row_end.  Once in a
+ * while, if the window is visible, the screen contents is drawn.
+ *
+ * If the terminal window has keyboard focus, typed keys are converted to the
+ * terminal encoding and writting to the job over a channel.
+ *
+ * If the job produces output, it is written to the VTerm.
+ * This will result in screen updates.
+ *
+ * TODO:
+ * - +terminal in features[] in version.c
+ * - free b_term when closing terminal.
+ * - remove term from first_term list when closing terminal.
+ * - set buffer options to be scratch, hidden, nomodifiable, etc.
+ * - set buffer name to command, add (1) to avoid duplicates.
+ * - command line completion (command name)
+ * - support fixed size when 'termsize' is "rowsXcols".
+ * - support minimal size when 'termsize' is "rows*cols".
+ * - support minimal size when 'termsize' is empty.
+ * - implement ":buf {term-buf-name}"
+ * - implement term_getsize()
+ * - implement term_setsize()
+ * - implement term_sendkeys()		send keystrokes to a terminal
+ * - implement term_wait()		wait for screen to be updated
+ * - implement term_scrape()		inspect terminal screen
+ * - implement term_open()		open terminal window
+ * - implement term_getjob()
+ */
+
+#include "vim.h"
+
+#ifdef FEAT_TERMINAL
+
+#include "libvterm/include/vterm.h"
+
+/* typedef term_T in structs.h */
+struct terminal_S {
+    term_T	*tl_next;
+
+    VTerm	*tl_vterm;
+    job_T	*tl_job;
+
+    /* Range of screen rows to update.  Zero based. */
+    int		tl_dirty_row_start; /* -1 if nothing dirty */
+    int		tl_dirty_row_end;   /* row below last one to update */
+
+    pos_T	tl_cursor;
+};
+
+#define MAX_ROW 999999	    /* used for tl_dirty_row_end to update all rows */
+
+/*
+ * List of all active terminals.
+ */
+static term_T *first_term = NULL;
+
+static int handle_damage(VTermRect rect, void *user);
+static int handle_moverect(VTermRect dest, VTermRect src, void *user);
+static int handle_movecursor(VTermPos pos, VTermPos oldpos, int visible, void *user);
+static int handle_resize(int rows, int cols, void *user);
+
+static VTermScreenCallbacks screen_callbacks = {
+  handle_damage,	/* damage */
+  handle_moverect,	/* moverect */
+  handle_movecursor,	/* movecursor */
+  NULL,			/* settermprop */
+  NULL,			/* bell */
+  handle_resize,	/* resize */
+  NULL,			/* sb_pushline */
+  NULL			/* sb_popline */
+};
+
+/*
+ * ":terminal": open a terminal window and execute a job in it.
+ */
+    void
+ex_terminal(exarg_T *eap)
+{
+    int		rows;
+    int		cols;
+    exarg_T	split_ea;
+    win_T	*old_curwin = curwin;
+    typval_T	argvars[2];
+    term_T	*term;
+    VTerm	*vterm;
+    VTermScreen *screen;
+
+    if (check_restricted() || check_secure())
+	return;
+
+    term = (term_T *)alloc_clear(sizeof(term_T));
+    if (term == NULL)
+	return;
+    term->tl_dirty_row_end = MAX_ROW;
+
+    /* Open a new window or tab. */
+    vim_memset(&split_ea, 0, sizeof(split_ea));
+    split_ea.cmdidx = CMD_new;
+    split_ea.cmd = (char_u *)"new";
+    split_ea.arg = (char_u *)"";
+    ex_splitview(&split_ea);
+    if (curwin == old_curwin)
+    {
+	/* split failed */
+	vim_free(term);
+	return;
+    }
+
+    curbuf->b_term = term;
+    term->tl_next = first_term;
+    first_term = term;
+
+    /* TODO: set buffer type, hidden, etc. */
+
+    if (*curwin->w_p_tms != NUL)
+    {
+	char_u *p = vim_strchr(curwin->w_p_tms, 'x') + 1;
+
+	rows = atoi((char *)curwin->w_p_tms);
+	cols = atoi((char *)p);
+	/* TODO: resize window if possible. */
+    }
+    else
+    {
+	rows = curwin->w_height;
+	cols = curwin->w_width;
+    }
+
+    vterm = vterm_new(rows, cols);
+    term->tl_vterm = vterm;
+    screen = vterm_obtain_screen(vterm);
+    vterm_screen_set_callbacks(screen, &screen_callbacks, term);
+
+    argvars[0].v_type = VAR_STRING;
+    argvars[0].vval.v_string = eap->arg;
+    argvars[1].v_type = VAR_UNKNOWN;
+    term->tl_job = job_start(argvars);
+
+    /* TODO: setup channels to/from job */
+    /* Setup pty, see mch_call_shell(). */
+}
+
+    static int
+handle_damage(VTermRect rect, void *user)
+{
+    term_T *term = (term_T *)user;
+
+    term->tl_dirty_row_start = MIN(term->tl_dirty_row_start, rect.start_row);
+    term->tl_dirty_row_end = MAX(term->tl_dirty_row_end, rect.end_row);
+    return 1;
+}
+
+    static int
+handle_moverect(VTermRect dest, VTermRect src, void *user)
+{
+    /* TODO */
+    return 1;
+}
+
+  static int
+handle_movecursor(VTermPos pos, VTermPos oldpos, int visible, void *user)
+{
+    /* TODO: handle moving the cursor. */
+    return 1;
+}
+
+    static int
+handle_resize(int rows, int cols, void *user)
+{
+    /* TODO: handle terminal resize. */
+    return 1;
+}
+
+/* TODO: Use win_del_lines() to make scroll up efficient. */
+
+/* TODO: function to update the window.
+ * Get the screen contents from vterm with vterm_screen_get_cell().
+ * put in current_ScreenLine and call screen_line().
+ */
+
+/* TODO: function to wait for input and send it to the job.
+ * Return when a CTRL-W command is typed that moves to another window.
+ * Convert special keys to vterm keys:
+ * - Write keys to vterm: vterm_keyboard_key()
+ * - read the output (xterm escape sequences): vterm_output_read()
+ * - Write output to channel.
+ */
+
+/* TODO: function to read job output from the channel.
+ * write to vterm: vterm_input_write()
+ * This will invoke screen callbacks.
+ * call vterm_screen_flush_damage()
+ */
+
+#endif /* FEAT_TERMINAL */