Attribute Errors Occured, unable to find attribute.

[WaylanPunch]

attrs.xml content:

<!-- FlatButton -->
    <declare-styleable name="fl_FlatButton">
        <attr name="fl_theme" />
        <attr name="fl_fontFamily" />
        <attr name="fl_fontWeight" />
        <attr name="fl_fontExtension" />
        <attr name="fl_textAppearance" />
        <attr name="fl_cornerRadius" />
        <attr name="fl_touchEffect" />

        <!-- Defines the height of the border bottom of the button -->
        <attr name="fl_blockButtonEffectHeight" format="dimension" />
    </declare-styleable>

And Errors Below Shew Up:

ERROR: In <declare-styleable> fl_FlatButton, unable to find attribute fl_theme
ERROR: In <declare-styleable> fl_FlatButton, unable to find attribute fl_touchEffect
ERROR: In <declare-styleable> fl_FlatButton, unable to find attribute fl_cornerRadius
ERROR: In <declare-styleable> fl_FlatButton, unable to find attribute fl_fontExtension
ERROR: In <declare-styleable> fl_FlatButton, unable to find attribute fl_fontFamily
ERROR: In <declare-styleable> fl_FlatButton, unable to find attribute fl_fontWeight
ERROR: In <declare-styleable> fl_FlatButton, unable to find attribute fl_textAppearance

In this file, there are also other declare-styleable items, and nothing bad happens to them, only this code snippet can't fit in. So Why?