Dunno! This is literal terra incognito to me! But wikipedia has this to say on the subject: (some basics)
Rights issue - Wikipedia
Stock dilution
Rights offerings offset the
dilutive effect of issuing more shares. For this reason, stock-exchange rules don't require that shareholders approve rights offerings if the company offers at least 20% of outstanding shares at a discount.
[1]:1 Because rights offerings are unpopular, companies typically choose them as a last resort, perhaps due to insufficient investor demand.
[2]
Tax treatment in the United States
If rights are exercised, they aren't taxed. Like with an ordinary security purchase, taxation happens when the security is sold. The cost basis of the shares is "the subscription price plus the tax basis for the exercised rights".
[3] The holding period begins at the time of exercise.
[3][4]
If rights are let to expire, they don't count as a deductible loss,
[3] as they have no tax basis in this case.
[4]