ggplot fails to put numbers in italic in facet title-CodePudding

I am trying to have some of my facets in italic text, at which point I noticed that my numbers do not become italic. I noticed the same behaviour in axis labels. Importantly, only partial parts of the labels or only some facets should be italic.

Is there any way to circumvent/fix this?

MWE:

library(ggplot2)
library(tibble)
tibble(
    a = c('a1~italic(a1)', 'Not~Italic'),
    x = c(1,1),
    y = c(1,1)
) %>% 
    ggplot(aes(x,y))   
    geom_point()  
    facet_grid(a~., labeller = label_parsed)   
    theme(
        strip.text = element_text(size = 20)
    )  
    xlab(expression(italic(Italic~part~of~label1)~not~italic~part~of~label1))

^{Created on 2022-03-02 by the}

First answer: Here is how we could do it using element_text():

library(ggplot2)
library(tibble)

tibble(
  a = 'a1a1',
  x = 1,
  y = 1
) %>% 
  ggplot(aes(x,y))   
  geom_point()  
  facet_grid(a~.) 
  theme(
    strip.text.y = element_text(
      size = 12, face = "italic")
    )