The following piece of code runs without error:

from selenium import webdriver
from selenium.webdriver import ChromeOptions
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
from selenium.webdriver.common.by import By

options = ChromeOptions()
options.add_argument("--headless")

selectors = [
    'img[alt=Google]',
    'img[alt="Google"]'
]

with webdriver.Chrome(options=options) as driver:
    driver.get("https://www.google.com")
    wait = WebDriverWait(driver, 5)
    for selector in selectors:
        t = By.CSS_SELECTOR, selector
        wait.until(EC.presence_of_element_located(t))

Note the two slightly different forms of CSS selector.

I have always understood that the definitive syntax for this would be:

'img[alt="Google"]'

Note the double-quotes.

I have determined that in selenium 4.22.0 (Python 3.12.4) the following syntax also works:

'img[alt=Google]'

Not the absence of double-quotes.

So my question is whether leaving out the double-quotes complies with CSS standards or is this something peculiar to selenium?