separator

A separator is a simple widget that has no behaviour in response to the user and renders itself as a line (either horizontal or vertical.) It's used to separate parts of a GUI.

See Ttk, a part of Tk 8.5, for a core widget set that includes a separator. Its documentation can be found at https://www.tcl-lang.org/man/tcl8.5/TkCmd/ttk_separator.htm .

A separator can be rendered by a single frame suitably packed or grided:

 proc separator {path} {
    return [frame $path -relief groove -borderwidth 2 -width 2 -height 2]
 }

 # Horizontal separator
 pack [separator .sep] -fill x

2014-09-24: I find the following definitions work better and look nicer. And they're not too expensive (Ni!).

(Nomenclature: to me, a horizontal separator is one that looks like a horizontal line but stacks vertically between other widgets.)

proc hseparator path {
    frame $path -relief flat -borderwidth 3 -height 0 -pady 0
    pack [frame $path.inner -relief groove -borderwidth 2 -height 2 -pady 0] -expand yes -fill x
    set path
}

# grid it:
grid [button .a -text abc] -sticky ew
grid [hseparator .sep]     -sticky ew
grid [button .b -text def] -sticky ew

# pack it:
pack [button .a -text abc]
pack [hseparator .sep] -fill x
pack [button .b -text def]

The result of gridding / packing isn't quite the same, since the gridded separator will stretch to the width of the other widgets, while a packed separator stretches to the width of the window.

proc vseparator {path} {
    frame $path -relief flat -borderwidth 3 -width 0 -padx 0
    pack [frame $path.inner -relief groove -borderwidth 1 -width 0 -padx 0] -expand yes -fill both
    pack [label $path.inner.lbl -text {} -borderwidth 0 -width 0 -padx 0]
    set path
}

# grid it:
grid [button .a -text abc] [vseparator .sep] [button .b -text def] -sticky w

# pack it:
pack [button .a -text abc] -side left
pack [vseparator .sep] -side left -fill y
pack [button .b -text def] -side left

Here, the result of gridding or packing is more or less the same, since the window will shrink to the height of the widgets.