I've analyzed the text and target items and constructed a regex pattern using alternation to match exactly the specified items.

The pattern is constructed with several distinct groups:
1. Scientific notation numbers: Captures "2.5e-10" and "-1.23E+4"
2. Base64 strings: Matches only the two specific base64 strings in the target list
3. Timestamps: Matches the three timestamp formats precisely
4. Quoted strings: Handles escaped quotes in both single and double quoted strings
5. Math expressions: Captures the mathematical formulas exactly as written
6. Quoted HTML-like elements: Matches only the specific nested quote formats with the correct content

Each part is separated with alternation (|) to match any of the target items. I've carefully escaped special regex characters like parentheses, plus signs, and other metacharacters to ensure they're matched literally.