And of course Cargo complains about my feature name only at publication time. Fixed.

speech-dispatcher/Cargo.toml

@@ -8,8 +8,8 @@ license = "LGPL-2.1 OR MIT OR Apache-2.0"
 edition = "2021"
 
 [features]
-"0.10" = []
-default = ["0.10"]
+0_10 = []
+default = ["0_10"]
 
 [dependencies]
 lazy_static = "1"

speech-dispatcher/src/lib.rs

@@ -98,7 +98,7 @@ pub enum Notification {
 #[repr(u32)]
 pub enum Punctuation {
     All = SPDPunctuation::SPD_PUNCT_ALL,
-    #[cfg(feature = "0.10")]
+    #[cfg(feature = "0_10")]
     Most = SPDPunctuation::SPD_PUNCT_MOST,
     Some = SPDPunctuation::SPD_PUNCT_SOME,
     None = SPDPunctuation::SPD_PUNCT_NONE,
@@ -413,25 +413,25 @@ impl Connection {
     }
 
     pub fn set_voice_type(&self, voice_type: VoiceType) -> Result<(), Error> {
-        #[cfg(feature = "0.10")]
+        #[cfg(feature = "0_10")]
         let v = unsafe { spd_set_voice_type(*self.0, voice_type as i32) };
-        #[cfg(not(feature = "0.10"))]
+        #[cfg(not(feature = "0_10"))]
         let v = unsafe { spd_set_voice_type(*self.0, voice_type as u32) };
         c_int_to_result(v)
     }
 
     pub fn set_voice_type_all(&self, voice_type: VoiceType) -> Result<(), Error> {
-        #[cfg(feature = "0.10")]
+        #[cfg(feature = "0_10")]
         let v = unsafe { spd_set_voice_type_all(*self.0, voice_type as i32) };
-        #[cfg(not(feature = "0.10"))]
+        #[cfg(not(feature = "0_10"))]
         let v = unsafe { spd_set_voice_type_all(*self.0, voice_type as u32) };
         c_int_to_result(v)
     }
 
     pub fn set_voice_type_uid(&self, voice_type: VoiceType, target_uid: u32) -> Result<(), Error> {
-        #[cfg(feature = "0.10")]
+        #[cfg(feature = "0_10")]
         let v = unsafe { spd_set_voice_type_uid(*self.0, voice_type as i32, target_uid) };
-        #[cfg(not(feature = "0.10"))]
+        #[cfg(not(feature = "0_10"))]
         let v = unsafe { spd_set_voice_type_uid(*self.0, voice_type as u32, target_uid) };
         c_int_to_result(v)
     }