要实现这个功能，我们可以利用Angular的自定义验证器来创建一个只允许第一行没有特殊字符的验证器。下面是一个例子：

首先在组件类中创建验证器：

import { FormControl, ValidatorFn, Validators } from '@angular/forms';

export const forbiddenFirstCharValidator: ValidatorFn = (control: FormControl) => {
  const forbidden = /^\s*[\!\@\#\$\%\^\&\*\(\)\+\=\[\]\{\}\\\|\;\:\'\"\,\.\<\>\/\?]\s*/.test(control.value.split('\n')[0]);
  return forbidden ? { 'forbiddenFirstChar': true } : null;
};

接着，在表单中使用验证器：

  

    The first line cannot start with a special character!
  

最后，为表单控件添加验证器：

import { Component } from '@angular/core';
import { FormGroup, FormControl, Validators } from '@angular/forms';
import { forbiddenFirstCharValidator } from './forbidden-first-char.validator';

@Component({
  selector: 'my-component',
  template: `
    

      
      

        

          The first line cannot start with a special character!
        
      
    
  `,
})
export class MyComponent {
  myForm = new FormGroup({
    'myTextArea': new FormControl('', [
      Validators.required,
      forbiddenFirstCharValidator
    ]),
  });