https://github.com/robotframework/seleniumlibrary/issues/672
没有内置函数，但可以使用：
创建关键字

Get child element

它需要两个参数parent（webelement）和child（xpath）来搜索父级中的子级。

Get child element    ${parent}    ./h3

假设父xpath为： //ul[@id="top_menu"] ，上面的代码将搜索相等的xpath //ul[@id="top_menu"]/./h3 注意taht上下文是父上下文而不是根上下文
所以这将等同于xpath

***Test Cases***

Google Search
    [Tags]    you    probably    do    not    have    this    many    tags    in    real    life
    Wait Until Element Is Visible  CSS=[id="introduction-container"]
    ${parent}=    Get webelement    xpath=//*[@id="introduction-container"]
    ${result}=    Get child element    ${parent}    ./h3   

***Keywords***

Get child element 
    [Arguments]    ${parent}   ${child} 
    ${child}=    Execute Javascript    return window.document.evaluate( arguments[1], arguments[0], null, XPathResult.FIRST_ORDERED_NODE_TYPE, null ).singleNodeValue;     ARGUMENTS    ${parent}    ${child}
    [Return]    ${child}