Encode space as _, change escape to __

README.md

@@ -46,18 +46,18 @@ $ tup
 
 Pokemon sprite filenames are in a 1-to-1 correspondence with the Pokemon's name, for ease of processing. Filenames may be directly substituted in shell commands without escaping. This naming scheme means that some of the filenames in `src/` are a little awkward looking to humans, but it means that no additional data beyond what is encoded in the filesystem is required to determine the correct name for any given Pokémon. 
 
-- Characters outside `[0-9a-zA-Z-.]` will be escaped using `_` and four hex characters, similar to JavaScript Unicode escapes. This conforms to the POSIX portable filename character set. (example: `Flabébé` -> `Flabe_0301be_0301`)
+Filenames must conform to the POSIX portable filename character set, `[0-9a-zA-Z-._]`. To ensure this, we encode filenames according to the following rules. Characters in `[0-9a-zA-Z-.]` are left as-is. Spaces are converted to an underscore. Other characters are escaped using two underscores and four hex characters, similar to JavaScript Unicode escapes. (example: `Flabébé` -> `Flabe__0301be__0301`)
 
     The following JS functions may be useful:
      ```javascript
     function encode(s) {
-        return s.replace(/[^0-9a-zA-Z-.]/g, c => '_' + c.charCodeAt(0).toString(16).padStart(4, '0'));
+        return s.replace(/[^0-9a-zA-Z-. ]/g, c => '__' + c.charCodeAt(0).toString(16).padStart(4, '0')).replace(" ", "_");
     }
     
     function decode(s) {
-        return s.replace(/_(....)/g, (_, m) => String.fromCharCode(parseInt(m, 16)));
+        return s.replace(/__(....)/g, (_, m) => String.fromCharCode(parseInt(m, 16))).replace("_", " ");
     }
-    ```
+```
 
 - Formes are separated with two dashes from their base. (example: `Necrozma--Dawn-Wings`)