What differences between QOpenGLFramebufferObject::bindDefault() and QOpenGLFramebufferObject::release()?

[Kiichiro]

Both methods have same description:

bq. Switches rendering back to the default, windowing system provided
framebuffer.
Returns true upon success, false otherwise.

Both doing same, but validation is differ. Why need two similar methods?

@bool QOpenGLFramebufferObject::bindDefault()
{
QOpenGLContext *ctx = const_cast<QOpenGLContext *>(QOpenGLContext::currentContext());
QOpenGLFunctions functions(ctx);

if (ctx) {
    ctx->d_func()->current_fbo = ctx->defaultFramebufferObject();
    functions.glBindFramebuffer(GL_FRAMEBUFFER, ctx->d_func()->current_fbo);

#ifdef QT_DEBUG
} else {
qWarning("QOpenGLFramebufferObject::bindDefault() called without current context.");
#endif
}

return ctx != 0;

}@

@bool QOpenGLFramebufferObject::release()
{
if (!isValid())
return false;

QOpenGLContext *current = QOpenGLContext::currentContext();
if (!current)
    return false;

Q_D(QOpenGLFramebufferObject);

#ifdef QT_DEBUG
if (current->shareGroup() != d->fbo_guard->group())
qWarning("QOpenGLFramebufferObject::release() called from incompatible context");
#endif

if (current) {
    current->d_func()->current_fbo = current->defaultFramebufferObject();
    d->funcs.glBindFramebuffer(GL_FRAMEBUFFER, current->d_func()->current_fbo);
}

return true;

}@