copula:::perspMvdc( )  中三个冒号似的符号表示什么意思？

某号后面这是个函数，一个叫叫Mvdc的函数。打算想知道改函数的调用方式、参数等说明文档，可以如下操作

function (x, FUN, xlim, ylim, n.grid = 26, xlab = "x1", ylab = "x2",
    zlab = deparse(substitute(FUN))[1], theta = -30, phi = 30,
    expand = 0.618, ticktype = "detail", ...)
{
    stopifnot(n.grid >= 2)
    if (length(n.grid) == 1)
        n.grid <- rep(n.grid, 2)
    stopifnot(length(n.grid) == 2)
    x. <- seq(xlim[1], xlim[2], length.out = n.grid[1])
    y. <- seq(ylim[1], ylim[2], length.out = n.grid[2])
    grid <- as.matrix(expand.grid(x = x., y = y., KEEP.OUT.ATTRS = FALSE))
    z.mat <- matrix(if (chkFun(FUN))
        FUN(grid, x)
    else FUN(x, grid), ncol = n.grid[2])
    T <- persp(x = x., y = y., z = z.mat, xlab = xlab, ylab = ylab,
        zlab = zlab, theta = theta, phi = phi, expand = expand,
        ticktype = ticktype, ...)
    invisible(list(x = x., y = y., z = z.mat, persp = T))
}

这是包里的内部函数。