These are all reasonable questions, but probably irrelevant for this kind of law: the law is not (necessarily) interested in determining a person's caste, but instead whether the defendant acted under a belief about a person's caste.

> - How is this implemented?

Don't know the actual proposal here, but almost certainly adds "caste" to the list of protected classes. Although it appears that "ancestry" is already an explicit protected class here: https://www.seattle.gov/civilrights/civil-rights-enforcement...

> - How is caste defined under American law? - Is there an enumerated list of all castes?

The US is a common law system, so the answer is "it doesn't matter, it's up to court interpretation."

> - How does one demonstrate under American law that person A is of caste X and person B is of caste Y?

This starts to get to the heart of the matter, what does a plaintiff have to show to be able to demonstrate discrimination on the basis of caste. My guess is that caste discrimination is already effectively covered by existing protected classes, but trying to convince a judge that the fact pattern is working towards establishing caste to thence be used for discrimination is likely to be exceedingly difficult at present. Add in "caste" as an explicit protected class, and, well, the plaintiff's job is much easier.

> - How is caste "assigned"? - Can one switch castes? Is ones caste immutable? - Does one register a caste like a political party?

These are all more or less irrelevant for the purposes of discrimination. It's the defendant (alleged discriminator)'s belief of the plaintiff's caste that matters. If that belief is incorrect, but was still used for the purposes of discrimination, it's illegal.

The thing someone is discriminated on the basis of doesn't need to be defined to make the discrimination illegal.

What matters is that the person who did the discrimination based it on the perceived characteristic of the person they discriminated against.

How do you know that someone is gay? Or an alcoholic? Or Dominican?

If someone believes that you’re a gay Dominican, but you’re actually a straight Puerto Rican, it’s not relevant. The action is the tort.

People are born in caste. One caste in one geographic area might have better prosperity than sane caste in other. People can leave religion, but in practice, never the caste. There are broad groups of castes, then sub groups, & more sub groups, & then numbers of layers of surnames. Father's cast goes to kids usually, but intercaste marriage usually gets the worse of both castes. Each side thinks the newly wed couple is not their member any more. Having money, power & reputation sometimes covers all the bad things of a caste. A high caste but poor person will face more difficulty than a super rich powerful politician of a lower caste.

To answer some :

1. Indian legal and governance systems maintain a list of recognized castes , these exists for reservation for government jobs, loans, elected seats[4] university admissions or promotions in government companies/departments - there are many problems with the list (outdated, lot of politically influenced changes ... )

2. Caste is hereditary, caste originated from family profession , somewhat akin to occupational surnames in some western countries like Smith [1]. Indian surnames also can indicate caste, the Self-Respect Movement from last century in the South evolved to drop surnames to reduce discrimination [2], and many people in parts of the country ended up use mononymous names.

3. Switching castes while occasionally practically possible was extremely hard, in the traditional orthodox system caste can be lost but not switched, typically lost when the parents are from different castes marry. In practice changing your profession or your son's profession would be the way to switch.

Education and vocational training however was denied back in olden days to keep it hereditary if you couldn't prove your caste background [3] you wouldn't be able to get a teacher or be apprenticed under a master. If you could get away by lying about it or someone from that caste vouched for you then yeah it could be changed.

4. Caste based registrations are a thing in India, mainly used to claim affirmative action in government

5. There is case law in Indian Juriprudence albeit in a different framework. Legal affirmative action frameworks(not the same as anti discriminatory approach in U.S law) are fraught with problems - Indian law has tons of problems of enforcing equitably.

[1] https://en.wikipedia.org/wiki/Category:Occupational_surnames

[2] https://en.wikipedia.org/wiki/Self-Respect_Movement

[3] A poignant story on this topic from mythology https://en.wikipedia.org/wiki/Ekalavya

[4] Election candidates in some areas are reserved to specific caste categories to represent the population better.

it doesn't matter. caste discrimination is very similar to racial discrimination - of course, race, as well as caste, has no strict definition under law. in fact, i would go as far as to say race cannot possibly be defined in a way that is useful.

to put it differently, if you don't actually belong to "race x", but fulfill someone's stereotype about "race x", you can still become a victim of racial discrimination.

the exact nature of what race or caste is, doesn't matter at all - it's the intent to exclude people based on one's preconceived notions of caste/race that does.