title: Scrapy - Activating an Item Pipeline component - ITEM_PIPELINES setting
body: <p>In scrapy documentation there is this information:</p>
  
  <blockquote>
    <p><strong>Activating an Item Pipeline component</strong></p>
    
    <p>To activate an Item Pipeline component you must add its class to the
    ITEM_PIPELINES setting, like in the following example:</p>
    
    <p>ITEM_PIPELINES = {
        'myproject.pipelines.PricePipeline': 300,
        'myproject.pipelines.JsonWriterPipeline': 800, }</p>
    
    <p>The integer values you assign to classes in this setting determine the
    order they run in- items go through pipelines from order number low to
    high. It’s customary to define these numbers in the 0-1000 range.</p>
  </blockquote>
  
  <p>I do not understand the last paragraph, mainly "determine the
   order they run in- items go through pipelines from order number low to
   high", can you explain in other words? that numbers are chosen because of what? in the range is 0-1000 how to choose the values?</p>