Gulp 4.0.0 + SASS, minification, TailwindCSS, PHP and BrowserSync support

gulpfile.js

"use strict";

// Gulp 4.0.0 + SASS, minification, TailwindCSS, PHP and BrowserSync support
// (assumes you have your .scss + .css files in a /css directory)
// william@wturrell.co.uk

var gulp        = require('gulp'),
    sass        = require('gulp-sass'),
    cssnano     = require('gulp-cssnano'),
    php         = require('gulp-connect-php'),
    browserSync = require('browser-sync');

var postcss     = require('gulp-postcss');
var tailwindcss = require('tailwindcss');
var reload      = browserSync.reload;

gulp.task('test', function() {
    console.log('Hello World!');
});

gulp.task('css', function(){
    return gulp.src('css/*.scss')
        // Use gulp-sass to convert SCSS to CSS
        .pipe(sass())
        .pipe(postcss([
            // https://tailwindcss.com/docs/installation/#4-process-your-css-with-tailwind
            tailwindcss('./path/to/your/tailwind.js'),
            require('autoprefixer')]))
        // minimise
        .pipe(cssnano())
        // write file to disk
        .pipe(gulp.dest('css'))
        // refresh browser
        .pipe(reload({
                stream: true
            })
        );
});

// Troubleshooting - you should see CLI debug messages for both the
// PHP Development server (port 8000) and BrowserSync (ports 3000 + 3001)
// if PHP's base directory is specified wrong, the whole thing can just hang

gulp.task('default', function() {
    php.server({
        // a standalone PHP server that browsersync connects to via proxy
        port: 8000,
        keepalive: true
    }, function (){
        browserSync({
            proxy: '127.0.0.1:8000'
        });
    });

    gulp.watch('**/*.html').on('change', function () {
        reload();
    });
    gulp.watch('**/*.php').on('change', function () {
        reload();
    });

    // the CSS task does it's own reloading
    gulp.watch("css/*.scss", gulp.series('css'));
});

could you explain line 27? why do we need to link js for CSS?

   gulp.watch('**/*.html').on('change', function () {
        reload();
    });
    gulp.watch('**/*.php').on('change', function () {
        reload();
    });

to

gulp.watch(['**/*.php','**/*.html']).on('change', function () {
        reload();
    });