How to understand definition of tensor $A$ in Weitzenböck identity

Question

I want to understand Weitzenbock identity in the case of Riemannian manifold. I looked at wiki article about it and I can't understand the definition of $$A=\frac{1}{2}\langle R(\theta,\theta)\#,\#\rangle+Ric(\theta,\#).$$ In wiki we read that

• $R$ is Riemann curvature tensor,
• $Ric$ is the Ricci tensor,
• $\theta:T^*M\otimes\Omega^pM\to\Omega^{p+1}M$ is the map that takes the wedge product of a 1-form and p-form and gives a (p+1)-form,
• $\#:\Omega^{p+1}M\to T^*M\otimes\Omega^pM$ is the universal derivation inverse to θ on 1-forms

Since Weitzenbock identity states that $$\Delta-\Delta'=A$$ I see that $A:\Omega^pM\to\Omega^pM$ for every $p.$

From wiki description of $\theta$ i guess that $\theta=\wedge$ and $\#$ looks very mysterious to me (even though I know Kahler differential (aka universal derivations)).

1. Can you explain what $\theta$ and $\#$ are?
2. How to evaluate $\langle R(\theta,\theta)\#,\#\rangle\eta$ and $Ric(\theta,\#)\eta$ where $\eta$ is a p-form?
3. Can you provide references where I can find such approach to Weitzenbock identity?