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To detect and protect confidential documents, we need a custom rule to identify project codes that start with 999 (since they are classified as confidential).

Box 1: A Sensitive Info Type (SIT) allows Microsoft Purview DLP policies to recognize structured data (e.g., project codes). DLP policies require a sensitive info type to detect content based on patterns, keywords, or dictionary terms. A sensitivity label alone does not define detection logic—it is used for classification and protection after content is identified.

Box 2: Since project codes follow a structured 10-digit pattern, we should use a Regular Expression (Regex) to match project codes that start with 999.

Example Regex pattern:

999\d{7}

This pattern detects a 10-digit number starting with "999".