More explanation on man page

man/man1/fzf.1

@@ -1149,8 +1149,19 @@ with the given string. An anchored-match term is also an exact-match term.
 .SS Exact\-boundary\-match (quoted both ends)
 A single-quoted term is interpreted as an "exact\-boundary\-match". fzf will
 search for the exact occurrences of the string with both ends at the word
+boundaries. Unlike in regular expressions, this also sees an underscore as
+a word boundary. But the words around underscores are ranked lower and appear
+later in the result than the other words around the other types of word
 boundaries.
 
+1. xxx foo xxx (highest score)
+.br
+2. xxx foo_xxx
+.br
+3. xxx_foo xxx
+.br
+4. xxx_foo_xxx (lowest score)
+
 .SS Negation
 If a term is prefixed by \fB!\fR, fzf will exclude the lines that satisfy the
 term from the result. In this case, fzf performs exact match by default.