Skip to content

Private Use Glyphs

Contour draws a few glyphs that Unicode has no character for. Rather than inventing a second drawing channel for them, they are given codepoints in a Private Use Area and rendered by the same built-in box-drawing renderer that draws U+2500–U+257F, the block elements and the legacy computing symbols.

This page documents those codepoints so that other terminals, fonts and tools can render the same glyphs if they want to. Nothing here is a protocol: no escape sequence introduces these characters, and Contour never requires an application to emit one.

The reserved block

U+10F000–U+10F0FF — Contour Terminal private glyphs.

The block sits in Supplementary Private Use Area-B (plane 16) rather than in the BMP's U+E000–U+F8FF. That lower range is comprehensively claimed by Nerd Fonts — Powerline, Font Awesome, Devicons, Octicons, Seti, Material and others — and Contour already renders several of those assignments itself (U+E0B0–U+E0BE, U+EE00–U+EE05, U+F5D0–U+F60D).

It also sits away from the start of a plane. An allocation that outgrows the BMP tends to land at the beginning of the next area it is offered, which makes U+F0000 — the first codepoint of plane 15 — one of the more contended places to put a block, not one of the safer ones. U+10F000 is near the far end of plane 16 instead, where no widely-deployed assignment reaches.

Only the codepoints listed below are actually claimed by the renderer. The rest of the block is reserved for future use and deliberately falls through to the font, so that reserving a range costs nothing to anyone who is already using it.

Assigned codepoints

Codepoint Name Glyph
U+10F000 FOLD HEAD OPEN A square box containing a minus, with a stem descending from its bottom edge to the bottom of the cell.
U+10F001 FOLD HEAD CLOSED A square box containing a plus. No stem.

Both are drawn as line art at the current foreground colour, scaled to the cell: the box is square whatever the cell's aspect ratio, and the stem shares its column with U+2502 so that the two meet exactly.

What they are for

They form the head of Contour's fold column — the gutter drawn to the left of the grid, which marks each foldable OSC 133 command block:

⊟─ $ make -j8          <- U+10F000, the block is open
│    [  1/120] cc a.c
│    [  2/120] cc b.c
┕    ... done          <- U+2515, the block's last row

⊞  $ make -j8          <- U+10F001, the block is collapsed

The body and tail need no private codepoints — U+2502 (BOX DRAWINGS LIGHT VERTICAL) and U+2515 (BOX DRAWINGS UP LIGHT AND RIGHT HEAVY) already describe them exactly.

The head does. U+229F SQUARED MINUS and U+229E SQUARED PLUS are the box and its sign, but neither carries the stem that joins an open head to the body beneath it, and a head that did not connect would read as two unrelated marks rather than as one bracket down the side of a block.

A box carrying a plus or a minus, rather than a triangle, because that is the fold control a reader has already met in editors, tree views and file managers.

Notes for implementers

  • These characters are produced by the terminal, for its own gutter. They are not part of any escape sequence, and an application has no reason to write one.
  • A Private Use Area assignment is by definition not exclusive. Planes 15 and 16 are also used by some East Asian fonts for user-defined characters (GB 18030 and Big5 user-defined areas), so a document that already uses U+10F000 for something else will render as a fold head in Contour. Turning the gutter off (folding.show_markers: false) does not change that, because the glyphs are claimed by the renderer rather than by the fold feature — if this ever proves to matter in practice, the claim is one entry in BoxDrawingRenderer::renderable().
  • If you implement these in a font, note that Contour will still prefer its own rendition: the box-drawing renderer is consulted before font shaping, and font.builtin_box_drawing: false turns that off for all built-in glyphs, not just these.