Given a character vector of model terms, checks to see which, if any, is the
model offset.

## Arguments

- terms
character vector of model terms.

## Value

A logical vector of the same length as `terms`

.

## Examples

```
load_mgcv()
df <- data_sim("eg1", n = 400, dist = "normal")
m <- gam(y ~ s(x0) + s(x1) + offset(x0), data = df, method = "REML")
nm <- names(model.frame(m))
nm
#> [1] "y" "offset(x0)" "x0" "x1"
is_offset(nm)
#> [1] FALSE TRUE FALSE FALSE
```