tbody structure is not detected

## Expected Result

I am parsing a table on an aspx webpage: https://www.ntuh.gov.tw/labmed/檢驗目錄/Lists/2015/BC.aspx. The `tr` elements are in a `tbody` structure. I expected to find them there.

## Actual Result

An empty list is returned as if there's nothing.

## Reproduction Steps

```python
import requests
from selenium import webdriver
from time import sleep
from lxml import etree, html

url = "https://www.ntuh.gov.tw/labmed/檢驗目錄/Lists/2015/BC.aspx"

# With selenium
browser = webdriver.Chrome()
browser.get(url)
# The url is visited with Chrome correctly
root = etree.fromstring(browser.page_source, etree.HTMLParser())
root.xpath("//table[@class='ms-listviewtable']/tbody/tr")
# It gives me several tr elements for further process

# With requests
result = ""
while result == "":
    try:
        # Certificate is not verified to bypass the SSLError
        # Not secure though
        result = requests.get(url, verify = False)
        break
    except:
        sleep(5)
        continue
# Transform it into an element tree
root = etree.fromstring(result.content, etree.HTMLParser())
# Parse the information with the same XPath
root.xpath("//table[@class='ms-listviewtable']/tbody/tr")
# It gives me an empty list
# However, this following line works:
root.xpath("//table[@class='ms-listviewtable']/tr")
```

I've also posted my question on Stack Overflow: [The same xpath yields different extraction results from the same webpage](https://stackoverflow.com/questions/49757013/the-same-xpath-yields-different-extraction-results-from-the-same-webpage).

## System Information

```shell
python -m requests.help
```

```
{
  "chardet": {
    "version": "3.0.4"
  },
  "cryptography": {
    "version": "2.2.1"
  },
  "idna": {
    "version": "2.6"
  },
  "implementation": {
    "name": "CPython",
    "version": "3.6.4"
  },
  "platform": {
    "release": "17.5.0",
    "system": "Darwin"
  },
  "pyOpenSSL": {
    "openssl_version": "100020ef",
    "version": "17.5.0"
  },
  "requests": {
    "version": "2.18.4"
  },
  "system_ssl": {
    "version": "100020ff"
  },
  "urllib3": {
    "version": "1.22"
  },
  "using_pyopenssl": true
}
```

Hi there! Thanks for opening this issue. Unfortunately, it seems this is a request for help instead of a report of a defect in the project. Please use [StackOverflow](https://stackoverflow.com) for general usage questions instead and only report defects here.

It looks like you also already posted to StackOverfow, so please be patient and wait for someone to answer you there.

Excuse me, but I don't know how you distinguish "request for help" from "report of a defect in the project". Can't "__`requests` is not able to recognize an existing html structure__" a defect which needs fixing? If not, could you give some clarification?

Hi @corytu, we don’t modify the html returned from the server. The issue you’re encountering is related to the server not returning content, or requiring JavaScript which Requests doesn’t support natively.

As @sigmavirus24 said, this is a usage question best suited for StackOverflow. You should be able to find a few other closed issues with questions about this as well. Thanks for checking in!

@corytu fundamentally you seem to be confusing HTTP with HTML. Requests handles HTTP. Users, like yourself, handle HTML.