Absolutely right. Yes, that means you're exempted from withholding the CPP and/or EI and/or PPIP. 

Because as per CRA:

- 'X' in CPP means your employer did not have to withhold CPP contributions from the earnings.

- 'X' in EI means only if your employer did not have to withhold EI premiums from the earnings for the entire reporting period.

- 'X' in PPIP means only if you did not have to withhold PPIP premiums from the earnings for the entire period of employment in the province of Quebec.

For more details, read Filling out the T4 slip by CRA.

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