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Unicode Script Exception Characters

A technical explanation of why certain script characters have non-contiguous Unicode code points and how this affects cursive font generation.

The Exception Character Problem

Why This Matters

When generating cursive fonts programmatically, most developers assume Unicode script characters are arranged in a simple, contiguous sequence. However, certain characters were assigned to Unicode positions long before the Mathematical Alphanumeric Symbols block was standardized. If you use simple offset arithmetic to map A-Z to their script equivalents, you'll generate mojibake (garbled text) for these exception characters.

Which Characters Are Exceptions?

Script Uppercase Exceptions

Letter	Unicode Code Point	Character	Why It's Different
B	U+212C	ℬ	Pre-existing in Letterlike Symbols block
E	U+2130	ℰ	Used in mathematical notation
F	U+2131	ℱ	Fourier transform symbol
H	U+210B	ℋ	Hamiltonian operator
I	U+2110	ℐ	Used in complex analysis
L	U+2112	ℒ	Laplace transform symbol
M	U+2133	ℳ	Used in mathematical physics
R	U+211B	ℛ	Riemann integral symbol

Script Lowercase Exceptions

Letter	Unicode Code Point	Character	Why It's Different
e	U+212F	ℯ	Euler's number (mathematical constant)
g	U+210A	ℊ	Used in physics notation
o	U+2134	ℴ	Order symbol (big O notation)
l	U+2113	ℓ	Liter symbol and angular momentum

Technical Implementation Requirements

The Wrong Way (Causes Mojibake)

// ❌ WRONG: Naive offset calculation
function toScript(char) {
  const code = char.charCodeAt(0);
  if (code >= 65 && code <= 90) { // A-Z
    return String.fromCodePoint(0x1D49C + (code - 65));
  }
  return char;
}

// Result for "HELLO":
// H → Wrong character (not ℋ)
// E → Wrong character (not ℰ)  
// L → Wrong character (not ℒ)

The Correct Way (Exception Map)

// ✓ CORRECT: Exception map + fallback
const scriptExceptions = {
  'B': '\u212C', 'E': '\u2130', 'F': '\u2131',
  'H': '\u210B', 'I': '\u2110', 'L': '\u2112',
  'M': '\u2133', 'R': '\u211B',
  'e': '\u212F', 'g': '\u210A',
  'o': '\u2134', 'l': '\u2113'
};

function toScript(char) {
  // MUST check exceptions first
  if (scriptExceptions[char]) {
    return scriptExceptions[char];
  }
  
  // Then apply standard offset
  const code = char.charCodeAt(0);
  if (code >= 65 && code <= 90) {
    return String.fromCodePoint(0x1D49C + (code - 65));
  }
  if (code >= 97 && code <= 122) {
    return String.fromCodePoint(0x1D4B6 + (code - 97));
  }
  return char;
}

// Result for "HELLO":
// H → ℋ (correct)
// E → ℰ (correct)
// L → ℒ (correct)

Critical Implementation Rule

Always check the exception map before applying any offset calculations. The exception characters must take priority over algorithmic mapping to prevent generating incorrect Unicode code points.

How This Affects Our Cursive Font Generator

Correct Exception Handling

Our tool implements proper exception character mapping using a lookup table before applying any offset calculations. This ensures that words like "HELLO," "BEFORE," "SMILE," and other common text containing B, E, F, H, I, L, M, R, e, g, o, or l are converted correctly without producing garbled Unicode.

Why Other Tools Fail

Many cursive font generators online use naive offset-based Unicode conversion without accounting for exception characters. This produces technically incorrect output that may render as wrong symbols or cause unexpected display behavior. Users often don't notice because the visual difference is subtle, but it violates Unicode standards and can cause issues with screen readers, search indexing, and platform filtering.

Impact on Compatibility Ratings

Fonts that correctly handle exception characters receive better stability ratings in our system. This is because proper Unicode mapping reduces the risk of platform filtering systems misidentifying the text as malformed or potentially malicious content.

Historical Context

Why Unicode Is Organized This Way

The Mathematical Alphanumeric Symbols block (U+1D400–U+1D7FF) was added to Unicode in version 3.1 (March 2001). However, many of the script characters had already been encoded in earlier Unicode versions for use in mathematical and scientific notation.

Rather than create duplicate code points, the Unicode Consortium designated these pre-existing characters as the canonical representations for script uppercase and lowercase letters. This maintains backwards compatibility with existing documents and prevents ambiguity in character encoding.

As a result, developers must use exception maps when implementing algorithmic font conversion. This is not a bug or inconsistency — it's an intentional design decision to preserve Unicode's stability and backwards compatibility.

For Developers Implementing Font Generators

Key Implementation Checklist

☑Create a complete exception character map for all script variants (bold, italic, etc.)
☑Always check exception map before applying offset arithmetic
☑Use String.fromCodePoint() instead of String.fromCharCode() for proper Unicode support
☑Test with words containing exception characters (HELLO, BEFORE, SMILE)
☑Verify output against official Unicode character tables
☑Document the exception handling in your code comments

Our Tool Handles Exceptions Correctly

Generate cursive fonts with proper Unicode exception character mapping

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