Update spec with Unicode escape sequences

Refined Unicode escape handling to support `\u{XXXXXX}` format, updated examples, ABNF grammar, and syntax highlighting rules. Enhanced test cases to validate new syntax and error scenarios. Drop \f and \b.

Author: antonmedv

.vitepress/maml.json

@@ -131,7 +131,7 @@
     "stringcontent": {
       "patterns": [
         {
-          "match": "\\\\(?:[\"/\\\\bfnrt]|u\\h{4})",
+          "match": "\\\\(?:[\"/\\\\nrt]|u\\{\\h{1,6}\\})",
           "name": "constant.character.escape.maml"
         },
         {

spec/v0.1.md

@@ -123,24 +123,23 @@ the control characters other than tab (U+0000 to U+0008, U+000A to U+001F,
 U+007F).
 
 ```maml
-"String with a \"nested\" string, \t tab, 😁 emoji, and \u0022 sequence"
+"String with a \"nested\" string, \t tab, 😁 emoji, and \u{10FFFF} sequence"
 ```
 
 For convenience, some popular characters have a compact escape sequence.
 
-```
-\b         - backspace       (U+0008)
-\t         - tab             (U+0009)
-\n         - linefeed        (U+000A)
-\f         - form feed       (U+000C)
-\r         - carriage return (U+000D)
-\"         - quote           (U+0022)
-\\         - backslash       (U+005C)
-```
+| Escape | Name            | Unicode  |
+|--------|-----------------|----------|
+| `\t`   | tab             | U+0009   |
+| `\n`   | linefeed        | U+000A   |
+| `\r`   | carriage return | U+000D   |
+| `\"`   | quote           | U+0022   |
+| `\\`   | backslash       | U+005C   |
+
 
-A Unicode character may be escaped with the `\uXXXX` form.
-The escape codes must be valid Unicode [scalar
-values](https://unicode.org/glossary/#unicode_scalar_value).
+A Unicode character may be escaped with the `\u{XXXXXX}` form. The hexadecimal 
+number can be from 1 to 6 digits long. The escape codes must be valid Unicode 
+[scalar values](https://unicode.org/glossary/#unicode_scalar_value).
 
 All other escape sequences not listed above are reserved; if they are used,
 MAML should produce an error. All strings must contain only valid UTF-8
@@ -202,7 +201,7 @@ All escape sequences are preserved as is.
 
 ```maml
 """
-There is no escaping, so \n, \u0022, etc.,
+There is no escaping, so \n, \u{0022}, etc.,
 are interpreted as-is without modification.
 """
 ```

spec/v0.1/maml.abnf

@@ -39,7 +39,7 @@ integer = "0" / ( onenine *DIGIT )
 quote = %x22
 
 char =  %x20-21 / %x23-5B / %x5D-10FFFF
-char =/ %x5C ( %x5C / quote / "/" / "b" / "f" / "n" / "r" / "t" / "u" 4HEXDIG )
+char =/ %x5C ( %x5C / quote / "/" / "n" / "r" / "t" / "u" "{" 1*6HEXDIG "}" )
 
 comment = "#" *non-eol
 

spec/v0.1/maml.test.js

@@ -112,10 +112,13 @@ describe('MAML v0.1', () => {
     parse(`"a"`)
     parse(`"\\n"`)
     parse(`"\\""`)
+    parse(`"\\u{10FFFF}"`)
 
     expect(() => parse(`"\\`)).toThrow()
     expect(() => parse(`"\n"`)).toThrow()
-    expect(() => parse(`"\\uGGGG"`)).toThrow()
+    expect(() => parse(`"\\u0000"`)).toThrow()
+    expect(() => parse(`"\\u{G}"`)).toThrow()
+    expect(() => parse(`"\\u{1234567}"`)).toThrow()
   })
 
   test('multiline string', () => {