To generate a new letter icon:

- Open `res/icons.sfd` in FontForge.
- Open "IBM Plex Sans Medium" to the side. Return to the icons font.
- Copy the (blank-looking) glyph at `E0F0` to the new codepoint. It contains two baselines.
- Open the new codepoint.
- Select the upper baseline.
- Use `Element | Insert Text Outlines...` to place text:
  - Turn off "Scale so text width matches path length".
  - Align "centered".
  - Type first line of text into the box.
  - Click the "Insert" button (might need window resize to be visible).
- Delete the upper baseline.
- If there's a second line of letters, repeat for the lower baseline.
- Delete the lower baseline.
- Select all.
- Use `Element | Transformations | Transform...` to scale and place the text:
  - For "Origin", select "Glyph Origin".
  - In the drop-down beneath that, select "Scale Uniformly", and beneath that, "Move". Fill in values as below:
    - One letter: 12000%, X 896, Y 15.5.
    - Two letters: 10000%, X 896, Y 99.2.
    - Three letters: 8000%, X 896, Y 183.
    - Two lines: 8000%, X 896, Y 618.5.
  - If resulting glyph is too wide, repeat all steps starting with "IBM Plex Sans Condensed Medium" instead.
    - Remember to close the other IBM Plex font or select the proper one in the "Insert Text Outlines..." dialog.
  - Hit `OK`. The letter icon should be properly sized and centered.
- Save.
- Use `File | Generate Fonts...` to export `res/icons.ttf`.
  - "Validate before saving" should be turned off.
  - An error will pop up informing that the TrueType em-size isn't a power of two. Ignore this.
- Run `res/make-iconfont.sh`.

Notes:

- Codepoints `E0F0` to `E0F4` are for reference only.
- The back layer of each of `E0F1` to `E0F4` has lines that show the expected tops and bottoms of text. Round letters and numerals will reach slightly above or below.
- The WSG icon (`E11F`) has been slightly kerned to fit.