clarify multi-line strings further

CHANGELOG.md

@@ -54,10 +54,10 @@
   * Around `=` for props (`x = 1`)
 * The BOM is now only allowed as the first character in a document. It was
   previously treated as generic whitespace.
-* Multi-line strings are now automatically dedented, according to the
-  least-indented line in the body. Multiline strings and raw strings now must
-  have a newline immediately following their opening `"`, and a final newline
-  preceding the closing `"`.
+* Multi-line strings are now automatically dedented, according to the common
+  whitespace matching the whitespace prefix of the closing line. Multiline
+  strings and raw strings now must have a newline immediately following their
+  opening `"`, and a final newline plus whitespace preceding the closing `"`.
 * SMALL EQUALS SIGN (`U+FE66`), FULLWIDTH EQUALS SIGN (`U+FF1D`), and HEAVY
   EQUALS SIGN (`U+1F7F0`) are now treated the same as `=` and can be used for
   properties (e.g. `お名前＝☜(ﾟヮﾟ☜)`). They are also no longer valid in bare

SPEC.md

@@ -436,30 +436,31 @@ The string contains the literal characters `hello\n\r\asd"#world`
 
 ### Multi-line Strings
 
-When a Quoted or Raw String spans multiple lines with literal, non-escaped Newlines,
-it follows a special multi-line syntax
-that automatically "dedents" the string,
-allowing its value to be indented to a visually matching level if desired.
-
-A Multi-line string _MUST_ start with a [Newline](#newline)
-immediately following its opening `"`.
-Its final line, preceding the closing `"`,
-_MUST_ contain only whitespace.
-All in-between lines that contain non-whitespace characters
-_MUST_ start with the exact same whitespace as the final line
-(precisely matching codepoints, not merely counting characters).
-
-The value of the Multi-line String omits the first and last Newline,
-the Whitespace of the last line,
-the matching Whitespace prefix on all intermediate lines,
-and all Whitespace on intermediate Whitespace-only lines.
-The first and last Newline can be the same character
-(that is, empty multi-line strings are legal).
+When a Quoted or Raw String spans multiple lines with literal, non-escaped
+Newlines, it follows a special multi-line syntax that automatically "dedents"
+the string, allowing its value to be indented to a visually matching level if
+desired.
+
+A Multi-line string _MUST_ start with a [Newline](#newline) immediately
+following its opening `"`. Its final line _MUST_ contain only whitespace,
+followed by a single closing `"`. All in-between lines that contain
+non-whitespace characters _MUST_ start with the exact same whitespace as the
+final line (precisely matching codepoints, not merely counting characters).
+
+The value of the Multi-line String omits the first and last Newline, the
+Whitespace of the last line, and the matching Whitespace prefix on all
+intermediate lines. The first and last Newline can be the same character (that
+is, empty multi-line strings are legal).
 
 Strings with literal Newlines that do not immediately start with a Newline and
-whose final `"` is not preceeded by optional whitespace and a Newline are illegal.
+whose final `"` is not preceeded by optional whitespace and a Newline are
+illegal.
 
-In other words, the final line specifies the whitespace prefix that will be removed from all other lines.
+In other words, the final line specifies the whitespace prefix that will be
+removed from all other lines.
+
+It is a syntax error for any body lines of the multi-line string to not match
+the whitespace prefix of the last line with the final quote.
 
 #### Example
 
@@ -526,6 +527,28 @@ A second indented paragraph.
 
 Equivalent to `"Indented a bit.\n\nA second indented paragraph."`
 
+-----------
+
+The following yield syntax errors:
+
+```kdl
+multi-line "
+  closing quote with non-whitespace prefix"
+```
+
+```kdl
+multi-line "stuff
+  "
+```
+
+```kdl
+// Every line must share the exact same prefix as the closing line.
+multi-line "[\n]
+[tab]a[\n]
+[space][space]b[\n]
+[space][tab][\n]
+[tab]"
+```
 
 ### Number
 

tests/test_cases/expected_kdl/multiline_raw_string_indented.kdl

@@ -0,0 +1,2 @@
+node "  hey\n everyone\n   how goes?"
+

tests/test_cases/expected_kdl/multiline_string_indented.kdl

@@ -0,0 +1,2 @@
+node "  hey\n everyone\n   how goes?"
+

tests/test_cases/input/multiline_raw_string_indented.kdl

@@ -0,0 +1,5 @@
+node #"
+    hey
+   everyone
+     how goes?
+  "#

tests/test_cases/input/multiline_raw_string_non_matching_prefix_character_error.kdl

@@ -0,0 +1,5 @@
+node #"
+    hey
+   everyone
+	   how goes?
+  "#

tests/test_cases/input/multiline_raw_string_non_matching_prefix_count_error.kdl

@@ -0,0 +1,5 @@
+node #"
+    hey
+ everyone
+     how goes?
+  "#

tests/test_cases/input/multiline_string_indented.kdl

@@ -0,0 +1,5 @@
+node "
+    hey
+   everyone
+     how goes?
+  "

tests/test_cases/input/multiline_string_non_matching_prefix_character_error.kdl

@@ -0,0 +1,5 @@
+node "
+    hey
+   everyone
+	   how goes?
+  "

tests/test_cases/input/multiline_string_non_matching_prefix_count_error.kdl

@@ -0,0 +1,5 @@
+node "
+    hey
+ everyone
+     how goes?
+  "