Function handler

packages/vite/src/node/plugins/css.ts:342–364

(id)

        id: CSS_LANGS_RE,
      },
      handler(id) {
        if (urlRE.test(id)) {
          if (isModuleCSSRequest(id)) {
            throw new Error(
              `?url is not supported with CSS modules. (tried to import ${JSON.stringify(
                id,
              )})`,
            )
          }

          // *.css?url
          // in dev, it's handled by assets plugin.
          if (isBuild) {
            id = injectQuery(removeUrlQuery(id), 'transform-only')
            return (
              `import ${JSON.stringify(id)};` +
              `export default "__VITE_CSS_URL__${Buffer.from(id).toString(
                'hex',
              )}__"`
            )
          }
        }
      },
    },
    transform: {
      filter: {