old_contents: from flask_wtf import FlaskForm
  from flask_wtf.file import FileField, FileRequired, FileAllowed
  from wtforms import StringField, TextAreaField
  from wtforms.fields.html5 import URLField, EmailField
  from wtforms.validators import InputRequired, URL, Regexp
  
  
  class NewLinkForm(FlaskForm):
      source_url = URLField('source_url', validators=[InputRequired(), URL()])
  
  class UploadForm(FlaskForm):
      file = FileField(validators=[
          FileRequired(),
          FileAllowed(['jpg', 'png', 'pdf'], 'Only JPEG, PNG and PDF are supported')
      ])
  
  class PosterForm(FlaskForm):
      title = StringField('title', validators=[InputRequired()])
      authors = StringField('authors', validators=[])
      abstract = TextAreaField('abstract', validators=[])
      download_url = URLField('download_url', validators=[InputRequired(), URL()])
      presented_at = StringField('presented_at', validators=[])
  
  class EmailForm(FlaskForm):
      email = EmailField('email', validators=[
          InputRequired(),
          Regexp('.+@.+', message='We are not too strict with emails, but at least put the "@" sign...'),
      ])
  
new_contents: from flask_wtf import FlaskForm
  from flask_wtf.file import FileField, FileRequired, FileAllowed
  from wtforms import StringField, TextAreaField
  from wtforms.fields.html5 import URLField, EmailField
  from wtforms.validators import InputRequired, URL, Regexp
  
  
  class NewLinkForm(FlaskForm):
      source_url = URLField('source_url', validators=[InputRequired(), URL()])
  
  class UploadForm(FlaskForm):
      file = FileField(validators=[
          FileRequired(),
          FileAllowed(['jpg', 'png', 'pdf'], 'Only JPG, PNG and PDF files are supported')
      ])
  
  class PosterForm(FlaskForm):
      title = StringField('title', validators=[InputRequired()])
      authors = StringField('authors', validators=[])
      abstract = TextAreaField('abstract', validators=[])
      download_url = URLField('download_url', validators=[InputRequired(), URL()])
      presented_at = StringField('presented_at', validators=[])
  
  class EmailForm(FlaskForm):
      email = EmailField('email', validators=[
          InputRequired(),
          Regexp('.+@.+', message='We are not too strict with emails, but at least put the "@" sign...'),
      ])
  
subject: fix form error msg