How I() function is used to build search bar feature with suggestion in this code any further explanation of the code (last two lines of ui)?

Question

Question

#This shinny app creates a search Bar feature which shows suggestions in real time as soon as user starts #typing in the search bar I don't have clear idea how the last part of the code works: " Any explanation of I() functions is used with dropdown and ontype in the last two lines of the "UI" part? is this R code or CSS code? any tutorial reference or readable source for such code will be appreciated.

library(shiny)

ui <- fluidPage(
  title = "Search Bar",
  fluidRow(
    selectizeInput(
      inputId = "searchme", 
      label = "Search Bar",
      multiple = FALSE,
      choices = c("Search Bar" = "", paste0(LETTERS,sample(LETTERS, 26))),
      options = list(
        create = FALSE,
        placeholder = "Search Me",
        maxItems = '1',
        onDropdownOpen = I("function($dropdown) {if (!this.lastQuery.length) {this.close(); this.settings.openOnFocus = false;}}"),
        onType = I("function (str) {if (str === \"\") {this.close();}}")
        )
      ))
  )

server <- function(input, output, session) {
  
  # Show Selected Value in Console
  observe({
    print(input$searchme)
  })
  }
shinyApp(ui, server)

I was trying to create search bar and found this code but could not understand the last two lines of the "ui' Part very well. is this R code or CSS code? any tutorial reference or readable source for such code will be appreciated.