You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: syntax.rs
    path of file: ./repos/lightningcss/src/values
    
    the code of the file until where you have to start completion: //! CSS syntax strings

use super::ident::Ident;
use super::number::{CSSInteger, CSSNumber};
use crate::error::{ParserError, PrinterError};
use crate::printer::Printer;
use crate::properties::custom::TokenL
    
  pub fn parse_string(input: &'i str) -> Result<SyntaxString, ()> {
    // https://drafts.css-houdini.org/css-properties-values-api/#parsing-syntax
    let mut input = input.trim_matches(SPACE_CHARACTERS);
    if input.is_empty() {
      return Err(());
    }

    if input == "*" {
      return Ok(SyntaxString::Universal);
    }

    let mut components = Vec::new();
    loop {
      let component = SyntaxComponent::parse_string(&mut input)?;
      components.push(component);

      input = input.trim_start_matches(SPACE_CHARACTERS);
      if input.is_empty() {
        break;
      }

      if input.starts_with('|') {
        input = &input[1..];
        continue;
      }

      return Err(());
    }

    Ok(SyntaxString::Components(components))
  }