Regex to ignore values that have a decimal point in front of value?

I have a dataset that looks like this:

> dput(test)
structure(list(Value = c("B20", "I82.B20", "B20, E88.1"), City = c("NY", 
"LA", "PA")), class = "data.frame", row.names = c(NA, -3L))

I want to extract the rows that have a corresponding value of 'B20', so I have the following code:

B20 <- test[grep(
  "B20",
  test$Value
),]

However, I do NOT want to include the rows where 'B20' is followed by a decimal point (such as row 2 (I82.B20)).

The following output should look like:

> dput(B20)
structure(list(Value = c("B20", "B20, E88.1"), City = c("NY", "PA")), row.names = c(NA, 3L), class = "data.frame")

The obvious solution is to select rows containing "B20" but exclude all rows including ".B20"

test[grepl("B20", test$Value) & !grepl("\\.B20", test$Value),]
#>        Value City
#> 1        B20   NY
#> 3 B20, E88.1   PA

Though if it has to be a single regex then you can match the start of the string ^ or any character that isn't a period [^\.] by combining these possibilities with (^|[^\.]). Then match B20, and for safety add a word boundary \b. Note we have to escape the backslashes, so the expression would be:

test[grep("(^|[^\\.])B20\\b", test$Value) ,]
#>        Value City
#> 1        B20   NY
#> 3 B20, E88.1   PA

I have to spend a little bit of time when I come across a regex like this to understand what's going on and think through the possible edge cases that might confound it, so in actual code I might prefer the first option even if it is a bit less "clever".