A more thorough explanation:

A witnessing part is a provision at the end of a legal document, such as a will, that is signed by witnesses. This provision confirms that the document was executed properly according to the laws of the jurisdiction where it will take effect.

For example, an attestation clause in a will might state that the testator (the person making the will) signed the document in the presence of two witnesses who also signed the document. This clause helps to ensure that the will is valid and can be probated (legally recognized) after the testator's death.

Another example of a witnessing part is a signature line for witnesses on a contract. By signing the contract as witnesses, the witnesses confirm that they saw the parties to the contract sign it and that they believe the signatures are genuine.