Explanation:

Article 20 dealing with Protection in respect of Conviction of offences has three provisions :

No ex-post-facto law: No person shall be (i) convicted of any offence except for violation of a law in force at the time of the commission of the act, nor (ii) subjected to a penalty greater than that prescribed by the law in force at the time of the commission of the act. An ex-post-facto law is one that imposes
penalties retrospectively (retroactively), that is, upon acts already done or which increases the penalties for such acts. However, this limitation is imposed only on criminal laws and not on civil laws or tax laws. In other words, a civil liability or a tax can be imposed retrospectively.

No double jeopardy: No person shall be prosecuted and punished for the same offence more than once. The protection against double jeopardy is available only in proceedings before a court of law or a judicial tribunal. In other words, it is not available in proceedings before departmental or administrative authorities as they are not of judicial nature.

No self-incrimination: No person accused of any offence shall be compelled to be a witness against himself. The protection against self-incrimination extends to both oral evidence and documentary evidence. Further, it extends only to criminal proceedings and not to civil proceedings or proceedings
which are not of criminal nature.