#include <bits/extc++.h>

using namespace std;
namespace rg = ranges;
namespace vw = views;

static inline void go(size_t), pre();

static constexpr size_t MN = 200, MK = 2 * MN - 1;

static bitset<MN> G[MN];
static bitset<MK> P, P1;
static size_t	  n, m, k;

int main()
{
	cin.tie(0)->sync_with_stdio(0);
	size_t T;
	cin >> T;
	for (size_t i = 0; i < T; i++)
		go(i);
}

void pre() {}

void go(size_t)
{
	cin >> n >> m;
	k = n + m - 2;
	P.reset();
	P1.reset();

	for (size_t u = 0; u <= k; u++)
		P1.set(u);

	for (size_t i = 0; i < n; i++)
		for (size_t j = 0, u = i; j < m; j++, u++)
		{
			char c;
			cin >> c;
			bool g	= (c == 'W');
			G[i][j] = g;
			P[u]	= P[u] ^ g;
		}

	bool odd = P[0];

	if (!(odd ? P == P1 : P.none()))
	{
		odd = !odd;
		for (size_t i = 0; i < n; i++)
			G[i].flip();
		for (size_t u = 0; u <= k; u++)
		{
			size_t len = n + m - (u > (n - 1) ? u - (n - 1) : (n - 1) - u) - (u > (m - 1) ? u - (m - 1) : (m - 1) - u);
			P[u] = P[u] ^ (((len + 1) / 2) & 1);
		}
	}

	if (!(odd ? P == P1 : P.none()))
	{
		cout << "NO\n";
		return;
	}
	cout << "YES\n" << k + odd << '\n';

	for (size_t ai = 0; ai < k; ai++)
	{
		size_t i = 0, j = 0, v = m - 1;
		G[0].flip(0);
		auto const R = [&]()
		{
			cout << 'R';
			j++;
			v--;
			G[i].flip(j);
		};
		auto const D = [&]()
		{
			cout << 'D';
			i++;
			v++;
			G[i].flip(j);
		};

		while (v > ai + 1)
			R();
		while (v < ai + 1)
			D();

		while (i < n - 1 & j < m - 1)
		{
			if (G[i][j + 1])
			{
				R();
				D();
			}
			else
			{
				D();
				R();
			}
		}
		while (i < n - 1)
			D();
		while (j < m - 1)
			R();
		cout << '\n';
	}
	if (odd)
	{
		cout << string(n - 1, 'D') << string(m - 1, 'R') << '\n';
	}
}

/*
4
3 3
WBB
BWB
BBW
1 5
WWWWW
2 2
BB
BB
4 1
W
B
B
W
*/