Dotenv libraries differ. EnvCheck accepts a small documented subset so a valid result stays understandable.
Names follow a portable pattern
A key starts with a letter or underscore and continues with letters, digits or underscores. Optional export must be followed by a normal assignment.
Quoted values must close on one line
Single and double quoted values are structurally checked, but their contents are never returned.
Expansion is deliberately excluded
${NAME}, command substitution, backticks and multiline continuations are rejected instead of interpreted.