(g) …provided, however, that…

A classic in drafting is the condition beginning with the proviso …provided, however, that… The words provided that makes the immediately preceding phrase conditional upon what follows after it.
An example of misusing provided that is:

If Purchaser becomes aware of a matter which gives rise to a Warranty Claim, it shall give prompt notice of the relevant facts to Seller; provided, however, that any failure to give such prompt notice shall not affect the rights of Purchaser unless Seller can demonstrate that such failure prejudiced Seller’s ability to successfully defend the matter giving rise to the Warranty Claim.

The proviso initiated by provided that is not a condition to what precedes but an exception. In the example, the words provided, however, that should therefore be replaced by except that. Alternatively, the exception could be considered redundant because if the failure to give timely notice does affect the Seller, such failure should remain for the account of Purchaser and be deductible from any amount eventually payable in connection with the Warranty Claim.

More provisos. Sometimes, two or even more conditions need to be identified. In such case, it is recommended to use a construct in which those two conditions are clearly identifiable. If one of those conditions can be reflected by only a few words (i.e., less than five words), separating the two by both and and is probably sufficient. If both conditions require more wording (e.g., each over seven words) it is recommended to initiate the second condition by …and provided furthermore, that… If more than two conditions apply, consider enumerating the clause.

Semicolon and underlining. In US stylish contracts, the proviso is sometimes initiated with a semicolon and the words provided and however are sometimes underlined for emphasis.

Broader scope of use. Historically, provided that was used as a truncation of the ‘term of enactment’ it is provided that, to introduce statutory provisions. (Compare the repetitive use of Whereas to introduce each recital of a contract or, for the French readers, the phrase Attendu que as used by the French Cour de cassation in its decisions.) In this broader explanation, the meaning of provided that is not necessarily limited to conditions but may also introduce exceptions, limitations and qualifications to the immediately preceding phrase. Or worse, it may even introduce a new provision that independent of the main clause. Consistent with normal parlance, it is recommended to reserve the words …provided that… for conditionality of clauses.