fix: allow punctuation for gsub context

.gitattributes

@@ -0,0 +1 @@
+*.png binary

README.md

@@ -2,13 +2,18 @@
 
 Injects a PNG logo into a TTF font as a ligature. Type a trigger sequence
 in any ligature-aware tool and the logo renders in place of the text. The
-replacement is context aware and will only trigger when the sequence is
-surrounded by whitespace.
+replacement is context aware and will only trigger when the sequence is not
+part of another number or string. Punctuation and whitespace may precede or
+follow the sequence.
 
 ```
 uv run font-lig --font input.ttf --logo cool.png --out output.ttf --sequence "cool" --family-name "Font + Cool"
+
+echo "Fonts are cool!"
 ```
 
+![example](./examples/fonts_are_cool.png)
+
 ## Existing Tools
 
 There are lots of ways to make your own font. I didn't see anything obvious and single-purpose to achieve this

main.py

@@ -283,15 +283,13 @@ def get_or_create_marker_glyph(font: TTFont, base_glyph: str) -> str:
     return marker
 
 
-def non_whitespace_glyphs(font: TTFont) -> list[str]:
+def alphanumeric_glyphs(font: TTFont) -> list[str]:
     """
-    Return glyph names for all non-whitespace characters in the font.
-    The ligature fires only when surrounded by whitespace or at a run boundary.
-
-    TODO: Are there other boundaries that may "trick" us?
+    Return glyph names for all alphanumeric characters in the font.
+    The ligature is suppressed when preceded/followed by a letter or digit.
     """
     cmap = font.getBestCmap() or {}
-    return [name for c, name in cmap.items() if not chr(c).isspace()]
+    return [name for c, name in cmap.items() if chr(c).isalnum()]
 
 
 def make_lig(glyph_name: str, components: list[str]) -> ot.Ligature:
@@ -393,7 +391,7 @@ def add_ligature(
     first_glyph = glyph_seq[0]
 
     if context:
-        exclusion_glyphs = non_whitespace_glyphs(font)
+        exclusion_glyphs = alphanumeric_glyphs(font)
         log.debug("context exclusion glyphs: %s", exclusion_glyphs)
 
         if exclusion_glyphs: