Add comment to describe camelcase line break

src/librustdoc/html/escape.rs

@@ -108,6 +108,16 @@ impl<'a> fmt::Display for EscapeBodyTextWithWbr<'a> {
                 || pk.map_or(true, |(_, t)| t.chars().any(|c| c.is_uppercase()));
             let next_is_underscore = || pk.map_or(true, |(_, t)| t.contains('_'));
             let next_is_colon = || pk.map_or(true, |(_, t)| t.contains(':'));
+            // Check for CamelCase.
+            //
+            // `i - last > 3` avoids turning FmRadio into Fm<wbr>Radio, which is technically
+            // correct, but needlessly bloated.
+            //
+            // is_uppercase && !next_is_uppercase checks for camelCase. HTTPSProxy,
+            // for example, should become HTTPS<wbr>Proxy.
+            //
+            // !next_is_underscore avoids turning TEST_RUN into TEST<wbr>_<wbr>RUN, which is also
+            // needlessly bloated.
             if i - last > 3 && is_uppercase() && !next_is_uppercase() && !next_is_underscore() {
                 EscapeBodyText(&text[last..i]).fmt(fmt)?;
                 fmt.write_str("<wbr>")?;