Funny strange (unicode) characters take more than one line

Understanding and Taming Zalgo Text: When Unicode Gets Wild

Explore the phenomenon of 'Zalgo text' – strange, multi-line unicode characters – and learn how to detect, prevent, and handle them in your applications.

Have you ever encountered text that seems to defy gravity, stretching across multiple lines or appearing as a garbled mess of overlapping symbols? This bizarre phenomenon is often referred to as 'Zalgo text,' a playful but sometimes problematic manifestation of Unicode's vast character set. While often used for comedic or artistic effect, Zalgo text can pose challenges for rendering engines, text processing, and user interfaces. This article delves into what Zalgo text is, how it's created, and practical strategies for dealing with it.

What is Zalgo Text?

Zalgo text is a form of text corruption that uses combining diacritical marks to stack characters vertically, creating an effect of distortion or 'corruption.' These combining characters are designed to modify the appearance of a base character (e.g., adding an accent mark). However, when many such marks are applied to a single base character, they can stack indefinitely, pushing the boundaries of how text is typically rendered. The name 'Zalgo' originates from a creepypasta meme, where a demonic entity 'corrupts' images and text.

flowchart TD
    A[Base Character] --> B{Apply Combining Diacritical Mark}
    B --> C[Modified Character]
    C -- Multiple Applications --> D[Zalgo Text (Vertical Stacking)]
    D --> E{Rendering Engine Challenges}
    E --> F[UI Overflow / Garbled Display]

How Zalgo text is formed and its impact on rendering.

The Unicode Behind the Madness

The magic (or madness) of Zalgo text lies in Unicode's extensive range of combining characters. These are characters that don't stand alone but attach to a preceding base character. Examples include accents, umlauts, and other diacritics. When a sequence of these combining characters is applied to a single letter, they stack on top and below it. Modern text rendering engines attempt to display these, but with enough combining characters, the stack can become arbitrarily tall, leading to the 'multi-line' effect. The key Unicode ranges often involved are U+0300–U+036F (Combining Diacritical Marks) and U+1DC0–U+1DFF (Combining Diacritical Marks Extended).

import unicodedata

def is_combining_char(char):
    # Check if a character is a combining character
    return unicodedata.category(char).startswith('M')

text = "H̷e̴l̷l̴o̸"
for char in text:
    print(f"'{char}': Combining: {is_combining_char(char)}")

# Example of creating Zalgo-like text
base_char = 'A'
combining_marks = "\u0308\u0308\u0308\u0308\u0308\u0308\u0308\u0308\u0308\u0308"
zalgo_a = base_char + combining_marks
print(f"\nZalgo 'A': {zalgo_a}")

Python code to identify combining characters and demonstrate Zalgo text creation.

Detecting and Sanitizing Zalgo Text

For applications that handle user-generated content, it's often necessary to detect and sanitize Zalgo text to prevent UI issues or abuse. The most common approach is to identify and remove excessive combining characters. A reasonable threshold for combining characters per base character is usually 1 or 2; anything beyond that is likely intentional Zalgo. You can iterate through the text, normalize it if necessary (e.g., using NFD form), and then count combining characters associated with each base character.

function sanitizeZalgo(text, maxCombining = 2) {
  let sanitizedText = '';
  let combiningCount = 0;

  for (let i = 0; i < text.length; i++) {
    const char = text[i];
    const charCode = char.charCodeAt(0);

    // Check if it's a combining character (Unicode category 'M')
    // This is a simplified check; a full implementation would use a library
    // or a more comprehensive range check for combining marks.
    const isCombining = (charCode >= 0x0300 && charCode <= 0x036F) ||
                        (charCode >= 0x1DC0 && charCode <= 0x1DFF);

    if (isCombining) {
      combiningCount++;
      if (combiningCount <= maxCombining) {
        sanitizedText += char;
      }
    } else {
      sanitizedText += char;
      combiningCount = 0; // Reset count for new base character
    }
  }
  return sanitizedText;
}

const zalgoInput = "H̷e̴l̷l̴o̸ W̷o̴r̷l̴d̸!\u0308\u0308\u0308\u0308\u0308";
console.log("Original: ", zalgoInput);
console.log("Sanitized (max 2): ", sanitizeZalgo(zalgoInput, 2));
console.log("Sanitized (max 0): ", sanitizeZalgo(zalgoInput, 0));

JavaScript function to sanitize Zalgo text by limiting combining characters.

Best Practices for Handling Unicode Input

To avoid issues with Zalgo text and other Unicode oddities, adopt robust input handling practices:

1. Normalize Input: Convert all incoming text to a consistent Unicode normalization form (e.g., NFC or NFD). This helps in consistent processing.
2. Validate Character Categories: Use unicodedata (Python) or similar libraries to inspect character categories. You can filter out characters that are not expected or are known to cause rendering issues.
3. Limit Combining Characters: Implement logic to count and limit the number of combining characters attached to any single base character.
4. Test with Edge Cases: Always test your input fields and rendering with various Unicode characters, including combining marks, emojis, and right-to-left scripts.
5. Use Appropriate Fonts: Ensure your application uses fonts that have good support for a wide range of Unicode characters and handle combining marks gracefully.

1. Step 1: Understand Unicode Normalization

Familiarize yourself with Unicode normalization forms (NFC, NFD, NFKC, NFKD). NFD separates base characters from their combining marks, making it easier to count and filter them.

2. Step 2: Implement a Sanitization Function

Write a function that iterates through input text. For each character, determine if it's a base character or a combining mark. Maintain a counter for consecutive combining marks. If the count exceeds a predefined threshold (e.g., 2), discard subsequent combining marks until a new base character is encountered.

3. Step 3: Apply Sanitization to User Input

Integrate your sanitization function into your application's input processing pipeline, especially for user-generated content like comments, usernames, or chat messages. This should happen before storage or display.

4. Step 4: Test Thoroughly

Create test cases with various Zalgo text examples, including those with many combining characters, and ensure your sanitization works as expected without affecting legitimate text.