#ifdef LOCAL
#define _GLIBCXX_DEBUG 1
#define dbg(...) cerr << "LINE(" << __LINE__ << ") -> [" << #__VA_ARGS__ << "]: [", DBG(__VA_ARGS__)
#else
#define dbg(...) 0
#endif

#if 0
    #include <ext/pb_ds/assoc_container.hpp>
    #include <ext/pb_ds/tree_policy.hpp>
 
    template<class T>
    using ordered_set = __gnu_pbds::tree<T, __gnu_pbds::null_type, std::less<T>, __gnu_pbds::rb_tree_tag,
        __gnu_pbds::tree_order_statistics_node_update>;
#endif

#include <vector> 
#include <list> 
#include <map> 
#include <set> 
#include <queue>
#include <stack> 
#include <bitset> 
#include <algorithm> 
#include <numeric> 
#include <utility> 
#include <sstream> 
#include <iostream> 
#include <iomanip> 
#include <cstdio> 
#include <cmath> 
#include <cstdlib> 
#include <ctime> 
#include <cstring>
#include <random>
#include <chrono>
#include <cassert>

using namespace std;
 
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define sz(x) (int)(x).size()
#define all(x) begin(x), end(x)
#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define F0R(i,a) FOR(i,0,a)
#define REP(i,n) for(int (i)=0;(i)<(int)(n);(i)++)

#define each(a,x) for (auto& a: x)
#define tcT template<class T
#define tcTU tcT, class U
#define tcTUU tcT, class ...U
template<class T> using V = vector<T>; 
template<class T, size_t SZ> using AR = array<T,SZ>;

typedef string str;
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
 
template<typename T, typename U> T &ctmax(T &x, const U &y){ return x = max<T>(x, y); }
template<typename T, typename U> T &ctmin(T &x, const U &y){ return x = min<T>(x, y); }
 
mt19937 rng((unsigned)chrono::steady_clock::now().time_since_epoch().count());
 
#define ts to_string
str ts(char c) { return str(1,c); }
str ts(bool b) { return b ? "true" : "false"; }
str ts(const char* s) { return (str)s; }
str ts(str s) { return s; }
str ts(vector<bool> v) { str res = "{"; F0R(i,sz(v)) res += char('0'+v[i]);	res += "}"; return res; }
template<size_t SZ> str ts(bitset<SZ> b) { str res = ""; F0R(i,SZ) res += char('0'+b[i]); return res; }
template<class A, class B> str ts(pair<A,B> p);
template<class T> str ts(T v) { bool fst = 1; str res = "{"; for (const auto& x: v) {if (!fst) res += ", ";	fst = 0; res += ts(x);}	res += "}"; return res;}
template<class A, class B> str ts(pair<A,B> p) {return "("+ts(p.first)+", "+ts(p.second)+")"; }
 
template<class A> void pr(A x) { cout << ts(x); }
template<class H, class... T> void pr(const H& h, const T&... t) { pr(h); pr(t...); }
void ps() { pr("\n"); }
template<class H, class... T> void ps(const H& h, const T&... t) { pr(h); if (sizeof...(t)) pr(" "); ps(t...); }
 
void DBG() { cerr << "]" << endl; }
template<class H, class... T> void DBG(H h, T... t) {cerr << ts(h); if (sizeof...(t)) cerr << ", ";	DBG(t...); }

tcTU> void re(pair<T,U>& p);
tcT> void re(V<T>& v);
tcT, size_t SZ> void re(AR<T,SZ>& a);

tcT> void re(T& x) { cin >> x; }
void re(double& d) { str t; re(t); d = stod(t); }
void re(long double& d) { str t; re(t); d = stold(t); }
tcTUU> void re(T& t, U&... u) { re(t); re(u...); }

tcTU> void re(pair<T,U>& p) { re(p.first,p.second); }
tcT> void re(V<T>& x) { each(a,x) re(a); }
tcT, size_t SZ> void re(AR<T,SZ>& x) { each(a,x) re(a); }
tcT> void rv(int n, V<T>& x) { x.rsz(n); re(x); }

constexpr bool multitest() {return 1;}
void solve();
int main() {
	ios_base::sync_with_stdio(false); cin.tie(NULL);
	int t = 1;
	if (multitest()) cin >> t;
	for (; t; t--) solve();
}



















vector<string> board;
int n, m;

string go(int x, int y) {
	string pa = "";
	board[0][0] ^= 1;
	for (int i = 1; i <= x; i++) {
		board[i][0] ^= 1;
		pa += "D";
	}
	for (int j = 1; j <= y; j++) {
		board[0][j] ^= 1;
		pa += "R";
	}

	while (x != n-1) {
		if (y == m-1) {
			board[++x][y] ^= 1;
			pa += "D";
		}
		else {
			if (board[x][y+1]) {
				board[x][++y] ^= 1;
				board[++x][y] ^= 1;
				pa += "RD";
			}
			else {
				board[++x][y] ^= 1;
				board[x][++y] ^= 1;
				pa += "DR";
			}
		}
	}

	while (y != m-1) {
		board[x][++y] ^= 1;
		pa += "R";
	}
	
	return pa;
} 

vector<string> dodo() {
	vector<string> paths;

	for (int i = m-2; i >= 0; i--) paths.push_back(go(0, i));
	for (int i = 1; i+1 < n; i++) paths.push_back(go(i, 0));

	if (board[0][0]) {
		string pa = "";
		for (int i = 0; i < n-1; i++) pa+="D";
		for (int i = 0; i < m-1; i++) pa+="R";
		for (int i = 0; i < n; i++) board[i][0] ^= 1;
		for (int j = 1; j < m; j++) board[n-1][j] ^= 1;
		paths.push_back(pa);
	}

	for (int i = 0; i < n; i++) {
		for (int j = 0; j < m; j++) {
			if (board[i][j]) {
				return {"no"};
			}
		}
	}

	return paths;
}

void solve() {
	re(n,m);
	board = vector<string>(n); re(board);

	for (int i = 0; i < n; i++) {
		for (int j = 0; j < m; j++) board[i][j]=(board[i][j]=='W');
	}

	vector<string> bd = board;

	vector<string> paths;
	if ((paths = dodo()) != vector<string>{"no"}) {
		ps("YES");
		ps(sz(paths));
		for (string s : paths) ps(s);
		return;
	}

	board = bd;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < m; j++) board[i][j] ^= 1;
	}
	
	if ((paths = dodo()) != vector<string>{"no"}) {
		ps("YES");
		ps(sz(paths));
		for (string s : paths) ps(s);
		return;
	}

	ps("NO");
}