How do I use variables with the delete command? (i.e., how to expand/reference variables for command arguments?)

Question

I'm using variables for line numbers, and I want to delete a range of lines using these variables. How do I do that?

    let x = 5
    let y = 20
    " I want to delete the range of lines from x to y (i.e., 5-20)
    " I guessed at this, but it doesn't work:
    x,ydelete
    " E15: Invalid expression: ",ydelete"

Extra credit for providing reference(s) to the vim documentation that explains this. (I searched the docs for "variable" but didn't find what I needed)

Answer 1

Use the :execute command, e.g.,

:execute x "," y "delete"

:exe[cute] {expr1} ..
Executes the string that results from the evaluation of {expr1} as an Ex command. Multiple arguments are concatenated...
{expr1} is used as the processed command

[:help execute]

Edit: Per D Ben Knoble's comment, How do I use a variable or return value in option, command, or mapping? addresses this question.