<function>glIsFramebuffer</function> returns <constant>GL_TRUE</constant> if <parameter>framebuffer</parameter> is currently the name of a framebuffer
object. If <parameter>framebuffer</parameter> is zero, or if <constant>framebuffer</constant> is not the name of a framebuffer object, or if an error
occurs, <function>glIsFramebuffer</function> returns <constant>GL_FALSE</constant>. If <parameter>framebuffer</parameter> is a name returned by
<citerefentry><refentrytitle>glGenFramebuffers</refentrytitle></citerefentry>, by that has not yet been bound through a call to
<citerefentry><refentrytitle>glBindFramebuffer</refentrytitle></citerefentry>, then the name is not a framebuffer object and <function>glIsFramebuffer</function>