docs: update explanation of .replace rule

docs/dictionary.md

@@ -509,11 +509,11 @@ each language. The number fragments are given in the `*_list` file.
 ## Character Substitution
 
 Character substitutions can be specified by using a `.replace` section
-at the start of the `*_rules` file. Each line specified either one or
-two alphabetic characters to be replaced by another one or two
-alphabetic characters. This substitution is done to a word before word is searched
+at the start of the `*_rules` file. In each line one character can be
+replaced by one or two characters. (Source and target of replacement can consume
+up to four bytes.) This substitution is done to a word _before_ word is searched
 in `*_list` or `*_listx` file and translated using the spelling-to-phoneme rules.
-Only the lower-case version of the characters needs to be specified. e.g.
+Only the lower-case version of the characters needs to be specified. e.g.:
 
 	.replace
 	   ô   ő   // (Hungarian) allow the use of o-circumflex instead of o-double-accute