Collapse all escape sequence rules into one (#743)

spec/message.abnf

@@ -1,8 +1,8 @@
 message           = simple-message / complex-message
 
 simple-message    = [simple-start pattern]
-simple-start      = simple-start-char / text-escape / placeholder
-pattern           = *(text-char / text-escape / placeholder)
+simple-start      = simple-start-char / escaped-char / placeholder
+pattern           = *(text-char / escaped-char / placeholder)
 placeholder       = expression / markup
 
 complex-message   = *(declaration [s]) complex-body
@@ -43,7 +43,7 @@ attribute      = "@" identifier [[s] "=" [s] (literal / variable)]
 
 variable       = "$" name
 literal        = quoted / unquoted
-quoted         = "|" *(quoted-char / quoted-escape) "|"
+quoted         = "|" *(quoted-char / escaped-char) "|"
 unquoted       = name / number-literal
 ; number-literal matches JSON number (https://www.rfc-editor.org/rfc/rfc8259#section-6)
 number-literal = ["-"] (%x30 / (%x31-39 *DIGIT)) ["." 1*DIGIT] [%i"e" ["-" / "+"] 1*DIGIT]
@@ -68,7 +68,7 @@ reserved-annotation-start = "!" / "%" / "*" / "+" / "<" / ">" / "?" / "~"
 private-use-annotation    = private-start [[s] reserved-body]
 private-start             = "^" / "&"
 reserved-body             = reserved-body-part *([s] reserved-body-part)
-reserved-body-part        = reserved-char / reserved-escape / quoted
+reserved-body-part        = reserved-char / escaped-char / quoted
 
 ; Names and identifiers
 ; identifier matches https://www.w3.org/TR/REC-xml-names/#NT-QName
@@ -101,10 +101,8 @@ content-char      = %x01-08        ; omit NULL (%x00), HTAB (%x09) and LF (%x0A)
                   / %xE000-10FFFF
 
 ; Character escapes
-text-escape     = backslash ( backslash / "{" / "}" )
-quoted-escape   = backslash ( backslash / "|" )
-reserved-escape = backslash ( backslash / "{" / "|" / "}" )
-backslash       = %x5C ; U+005C REVERSE SOLIDUS "\"
+escaped-char = backslash ( backslash / "{" / "|" / "}" )
+backslash    = %x5C ; U+005C REVERSE SOLIDUS "\"
 
 ; Whitespace
 s = 1*( SP / HTAB / CR / LF / %x3000 )

spec/syntax.md

@@ -158,7 +158,7 @@ An empty string is a valid _simple message_.
 
 ```abnf
 simple-message = [simple-start pattern]
-simple-start   = simple-start-char / text-escape / placeholder
+simple-start   = simple-start-char / escaped-char / placeholder
 ```
 
 A **_<dfn>complex message</dfn>_** is any _message_ that contains _declarations_,
@@ -264,7 +264,7 @@ Unless there is an error, resolving a _message_ always results in the formatting
 of a single _pattern_.
 
 ```abnf
-pattern = *(text-char / text-escape / placeholder)
+pattern = *(text-char / escaped-char / placeholder)
 ```
 A _pattern_ MAY be empty.
 
@@ -300,7 +300,7 @@ U+007B LEFT CURLY BRACKET `{`, and U+007D RIGHT CURLY BRACKET `}`
 MUST be escaped as `\\`, `\{`, and `\}` respectively.
 
 In the ABNF, _text_ is represented by non-empty sequences of
-`simple-start-char`, `text-char`, and `text-escape`.
+`simple-start-char`, `text-char`, and `escaped-char`.
 The first of these is used at the start of a _simple message_,
 and matches `text-char` except for not allowing U+002E FULL STOP `.`.
 The ABNF uses `content-char` as a shared base for _text_ and _quoted literal_ characters.
@@ -675,7 +675,7 @@ reserved-annotation       = reserved-annotation-start [[s] reserved-body]
 reserved-annotation-start = "!" / "%" / "*" / "+" / "<" / ">" / "?" / "~"
 
 reserved-body             = reserved-body-part *([s] reserved-body-part)
-reserved-body-part        = reserved-char / reserved-escape / quoted
+reserved-body-part        = reserved-char / escaped-char / quoted
 ```
 
 ## Markup
@@ -852,7 +852,7 @@ of number values in _operands_ or _options_, or as _keys_ for _variants_.
 
 ```abnf
 literal        = quoted / unquoted
-quoted         = "|" *(quoted-char / quoted-escape) "|"
+quoted         = "|" *(quoted-char / escaped-char) "|"
 unquoted       = name / number-literal
 number-literal = ["-"] (%x30 / (%x31-39 *DIGIT)) ["." 1*DIGIT] [%i"e" ["-" / "+"] 1*DIGIT]
 ```
@@ -934,14 +934,13 @@ An **_<dfn>escape sequence</dfn>_** is a two-character sequence starting with
 U+005C REVERSE SOLIDUS `\`.
 
 An _escape sequence_ allows the appearance of lexically meaningful characters
-in the body of _text_, _quoted_, or _reserved_ (which includes, in this case,
-_private-use_) sequences respectively:
+in the body of _text_, _quoted_, or _reserved_
+(which includes, in this case, _private-use_) sequences.
+Each _escape sequence_ represents the literal character immediately following the initial `\`.
 
 ```abnf
-text-escape     = backslash ( backslash / "{" / "}" )
-quoted-escape   = backslash ( backslash / "|" )
-reserved-escape = backslash ( backslash / "{" / "|" / "}" )
-backslash       = %x5C ; U+005C REVERSE SOLIDUS "\"
+escaped-char = backslash ( backslash / "{" / "|" / "}" )
+backslash    = %x5C ; U+005C REVERSE SOLIDUS "\"
 ```
 
 ### Whitespace