Uppercase to lowercase converter

Purpose & User Intent: This tool solves the problem of text casing by converting uppercase letters to lowercase while preserving digits, punctuation, symbols, and non-letter characters. It serves developers, content teams, translators, and data engineers who need consistent casing for storage, indexing, comparisons, and rendering. Common use cases include normalizing user input, preparing data for search, and cleaning logs for analytics.
Core Logic & Features: Core operation is a character-by-character Unicode case-mapping toLowerCase. Required features include reliable transformation, preservation of non-letter characters, determinism, and stateless processing. Optional/advanced features include locale-aware mappings, batch processing, API access, and handling of multi-codepoint case mappings.
Inputs & Outputs: Inputs include input_text (string), locale (optional string), and mode (optional). Outputs include lowercased_text (string). Validation rules: input_text must be a string; locale if provided must be a valid language tag; output length equals input length; non-letter characters are preserved.
Algorithms & Calculations: For each code point, apply Unicode case mapping to lowercase. ASCII letters A-Z map to a-z; non-letter code points either map to themselves or remain unchanged. The operation is idempotent; applying it again yields the same string. No external data fetch; performance is linear in input length.
Error & Edge Cases: Empty input returns empty output. Surrogate handling: well-formed inputs map cleanly; malformed surrogates can raise a strict mode error or be replaced depending on configuration. Extremely long strings are processed in streaming chunks in typical runtimes.
Industry/Region & Localization: Unicode-based casing supports global text; locale-aware mode enables language-specific rules via BCP47 tags (e.g., Turkish). Outputs are suitable for multi-region content, indexing, and search normalization in internationalized domains.
Assumptions & Exclusions: Assumes UTF-8 input; excludes translation, semantic processing, or tone adjustments; UI behavior, rate limits, and API access are outside scope; does not alter character width or layout.